Range extension mode for WiFi

ABSTRACT

A communication device encodes a plurality of information bits to generate a plurality of encoded bits, and maps the plurality of encoded bits to a plurality of constellation symbols, including mapping each bit to multiple constellation symbols. The communication device generates a plurality of orthogonal frequency division multiplexing (OFDM) symbols corresponding to a physical layer (PHY) data unit using the plurality of constellation symbols, wherein the OFDM symbols are generated such that: the OFDM symbols have a tone spacing that is ¼ of a tone spacing of a legacy wireless communication protocol, and the OFDM symbols span only a subband of a 20 MHz communication channel. The communication device generates a transmission signal using the plurality of OFDM symbols, the transmission signal spanning only the subband of the 20 MHz communication channel.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/523,678, entitled “Range Extension Mode for WiFi,” filed on Oct. 24,2014, which claims the benefit of U.S. Provisional Patent ApplicationNo. 61/895,591, entitled “Range Extension PHY,” filed on Oct. 25, 2013,U.S. Provisional Patent Application No. 61/925,332, entitled “RangeExtension PHY,” filed on Jan. 9, 2014, U.S. Provisional PatentApplication No. 61/950,727, entitled “Range Extension PHY,” filed onMar. 10, 2014, and U.S. Provisional Patent Application No. 61/987,778,entitled “Range Extension PHY,” filed on May 2, 2014. The disclosures ofeach of the applications referenced above are incorporated herein byreference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to wireless local area networks that utilize a rangeextension mode.

BACKGROUND

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in thegigabits per second (Gbps) range. Future standards promise to provideeven greater throughputs, such as throughputs in the tens of Gbps range.

SUMMARY

In an embodiment, a method is for generating a physical layer (PHY) dataunit for transmission via a communication channel, the PHY data unitconforming to an extended range mode of a wireless communicationprotocol. The method includes: encoding, at a communication device, aplurality of information bits to generate a plurality of encoded bits;mapping, at the communication device, the plurality of encoded bits to aplurality of constellation symbols, including mapping each bit tomultiple constellation symbols; and generating, at the communicationdevice, a plurality of orthogonal frequency division multiplexing (OFDM)symbols corresponding to the PHY data unit using the plurality ofconstellation symbols, wherein the OFDM symbols are generated such that:the OFDM symbols have a tone spacing that is ¼ of a tone spacing of alegacy wireless communication protocol, and the OFDM symbols span only asubband of a 20 MHz communication channel. The method also includesgenerating, at the communication device, a transmission signal using theplurality of OFDM symbols, the transmission signal spanning only thesubband of the 20 MHz communication channel.

In another embodiment, an apparatus comprises a network interface deviceimplemented using one or more integrated circuit (IC) devices. Thenetwork interface device includes: a media access control (MAC)processing unit configured to operate according to a communicationprotocol that defines an extended range mode, the MAC processing unitimplemented using the one or more IC devices, and a physical layer (PHY)processing unit coupled configured to operate according to thecommunication protocol, the PHY processing unit coupled to the MACprocessing unit and implemented using the one or more IC devices. ThePHY processing unit is configured to: encode a plurality of informationbits to generate a plurality of encoded bits; map the plurality ofencoded bits to a plurality of constellation symbols, including mappingeach bit to multiple constellation symbols; and generate a plurality oforthogonal frequency division multiplexing (OFDM) symbols correspondingto a PHY data unit using the plurality of constellation symbols, whereinthe PHY data unit conforms to the extended range mode, and wherein theOFDM symbols are generated such that: the OFDM symbols have a tonespacing that is ¼ of a tone spacing of a legacy wireless communicationprotocol, and the OFDM symbols span only a subband of a 20 MHzcommunication channel. The PHY processing unit is also configured togenerate a transmission signal using the plurality of OFDM symbols, thetransmission signal spanning only the subband of the 20 MHzcommunication channel, wherein the transmission signal corresponds tothe PHY data unit.

In yet another embodiment, a tangible, non-transitory computer readablemedium, or media, stores machine readable instructions that, whenexecuted by one or more processors, cause the one or more processors to:encode a plurality of information bits to generate a plurality ofencoded bits; map the plurality of encoded bits to a plurality ofconstellation symbols, including mapping each bit to multipleconstellation symbols; and generate a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols corresponding to physical layer(PHY) data unit using the plurality of constellation symbols, whereinthe PHY data unit conforms to an extended range mode of a wirelesscommunication protocol, and wherein the OFDM symbols are generated suchthat: the OFDM symbols have a tone spacing that is ¼ of a tone spacingof a legacy wireless communication protocol, and the OFDM symbols spanonly a subband of a 20 MHz communication channel. The tangible,non-transitory computer readable medium, or media, also stores machinereadable instructions that, when executed by one or more processors,cause the one or more processors to generate a transmission signal usingthe plurality of OFDM symbols, the transmission signal spanning only thesubband of the 20 MHz communication channel, wherein the transmissionsignal corresponds to the PHY data unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN), according to an embodiment.

FIGS. 2A and 2B are diagrams of a prior art data unit format.

FIG. 3 is a diagram of another prior art data unit format.

FIG. 4 is a diagram of another prior art data unit format.

FIG. 5 is a diagram of another prior art data unit format.

FIG. 6A is a group of diagrams of modulations used to modulate symbolsin a prior art data unit.

FIG. 6B is a group of diagrams of modulations used to modulate symbolsin an example data unit, according to an embodiment.

FIG. 7A is a diagram of an orthogonal frequency division multiplexing(OFDM) data unit, according to an embodiment.

FIG. 7B is a group of diagrams of modulations used to modulate symbolsin the data unit depicted in FIG. 7A, according to an embodiment.

FIG. 8 is a block diagram of an OFDM symbol, according to an embodiment.

FIG. 9A is a diagram illustrating an example data unit in which aregular coding scheme is used for a preamble of the data unit, accordingto an embodiment.

FIG. 9B is a diagram illustrating an example data unit in which aregular coding scheme is used for only a portion a preamble of the dataunit, according to an embodiment.

FIG. 10A is a diagram illustrating an example data unit in which tonespacing adjustment is used in combination with block coding, accordingto an embodiment.

FIG. 10B is a diagram illustrating an example data unit in which tonespacing adjustment is used in combination with block coding, accordingto another embodiment.

FIG. 11A is a diagram illustrating a regular mode data unit, accordingto an embodiment.

FIG. 11B is a diagram illustrating range extension mode data unit,according to an embodiment.

FIGS. 12A-12B are diagrams respectively illustrating two possibleformats of a long training field, according to two example embodiments.

FIG. 13A is a diagram illustrating a non-legacy signal field of theregular mode data unit of FIG. 11A, according to an embodiment.

FIG. 13B is a diagram illustrating a non-legacy signal field of therange extension mode data unit of FIG. 11B, according to an embodiment.

FIG. 14A is a block diagram illustrating a range extension mode dataunit, according to an embodiment.

FIG. 14B is a diagram illustrating a legacy signal field of the rangeextension mode data unit of FIG. 14A, according to one embodiment.

FIG. 14C is a diagram illustrating a Fast Fourier Transform (FFT) windowfor the legacy signal field of FIG. 14B at the legacy receiving device,according to an embodiment.

FIG. 15 is a block diagram illustrating format of a non-legacy signalfield, according to an embodiment.

FIG. 16 is a block diagram illustrating an example PHY processing unitfor generating regular mode data units using the regular coding scheme,according to an embodiment.

FIG. 17A is a block diagram of an example PHY processing unit forgenerating range extension mode data units using a range extensioncoding scheme, according to an embodiment.

FIG. 17B is a block diagram of an example PHY processing unit forgenerating range extension mode data units, according to anotherembodiment.

FIG. 18A is a block diagram of an example PHY processing unit forgenerating range extension mode data units using a range extensioncoding scheme, according to another embodiment.

FIG. 18B is a block diagram of an example PHY processing unit forgenerating range extension mode data units, according to anotherembodiment.

FIG. 19A is a block diagram of an example PHY processing unit forgenerating range extension mode data units, according to anotherembodiment.

FIG. 19B is a block diagram of an example PHY processing unit forgenerating range extension mode data units, according to anotherembodiment.

FIG. 20A is a diagram showing repetition of OFDM symbols in a preambleof a range extension mode data unit, according to an embodiment.

FIG. 20B is a diagram showing repetition of OFDM symbols in a preambleof a range extension mode data unit, according to an embodiment.

FIG. 20C is a diagram showing a time domain repetition scheme for OFDMsymbols, according to one embodiment.

FIG. 20D is a diagram showing a repetition scheme for OFDM symbols,according to another embodiment.

FIG. 21 is a flow diagram of an example method for generating a dataunit, according to an embodiment.

FIG. 22A is a diagram of a 20 MHz overall bandwidth having repetitionsof the range extension data unit having a 10 MHz sub-band, according toan embodiment.

FIG. 22B is a diagram of a 40 MHz overall bandwidth having repetitionsof the range extension data unit having a 10 MHz sub-band, according toan embodiment.

FIG. 22C is a diagram of an example tone plan for a 32-FFT mode,according to an embodiment.

FIG. 23 is a diagram of an example data unit in which the rangeextension mode is used for a preamble of the data unit, according to anembodiment.

FIG. 24 is a block diagram of an example PHY processing unit forgenerating range extension mode data units, according to anotherembodiment.

FIG. 25A is a diagram of an example 20 MHz total bandwidth having ½ tonespacing, according to an embodiment.

FIG. 25B is a diagram of an example 20 MHz total bandwidth having ½ tonespacing, according to an embodiment.

FIG. 26A is a diagram of a non-legacy tone plan for the range extensionmode having a size 64 FFT and ½ tone spacing, according to anembodiment.

FIG. 26B is a diagram of a non-legacy tone plan for the range extensionmode having a size 128 FFT and ½ tone spacing, according to anembodiment.

FIG. 26C is a diagram illustrating a non-legacy tone plan for the rangeextension mode having a size 256 FFT and ½ tone spacing, according to anembodiment.

FIG. 27 is a flow diagram of an example method for generating a dataunit, according to an embodiment.

FIG. 28 is a flow diagram of an example method for generating a dataunit, according to another embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The AP is configured to operatewith client stations according to at least a first communicationprotocol. The first communication protocol is sometimes referred toherein as “high efficiency Wi-Fi,” “HEW” communication protocol, or802.11ax communication protocol. In some embodiments, different clientstations in the vicinity of the AP are configured to operate accordingto one or more other communication protocols which define operation inthe same frequency band as the HEW communication protocol but withgenerally lower data throughputs. The lower data throughputcommunication protocols (e.g., IEEE 802.11a, IEEE 802.11n, and/or IEEE802.11ac) are collectively referred herein as “legacy” communicationprotocols. In at least some embodiments, the legacy communicationprotocols are generally deployed in indoor communication channels, andthe HEW communication protocol is at least sometimes deployed foroutdoor communications, extended range communications, or communicationsin areas with reduced signal-to-noise ratios (SNR) of transmittedsignals.

According to an embodiment, symbols transmitted by the AP are generatedaccording to a range extension coding scheme that provides increasedredundancy of symbols or information bits encoded within the symbols.The redundancy increases the likelihood of the symbols beingsuccessfully decoded by a device that receives the symbols from the AP,particularly in areas with reduced SNR. An amount of redundancy neededto mitigate the reduced SNR generally depends on a delay channel spread(e.g. for an outdoor communication channel), other signals thatinterfere with the symbols, and/or other factors. In an embodiment, theHEW communication protocol defines a regular mode and a range extensionmode. The regular mode is generally used with communication channelscharacterized by shorter channel delay spreads (e.g., indoorcommunication channels) or generally higher SNR values, while the rangeextension mode is generally used with communication channelscharacterized by relatively longer channel delay spreads (e.g., outdoorcommunication channels) or generally lower SNR values in an embodiment.In an embodiment, a regular coding scheme is used in the regular mode,and a range extension coding scheme is used in the range extension mode.

In an embodiment, a data unit transmitted by the AP includes a preambleand a data portion, wherein the preamble is used, at least in part, tosignal, to a receiving device, various parameters used for transmissionof the data portion. In various embodiments, the preamble of a data unitis used to signal, to a receiving device, the particular coding schemebeing utilized in at least the data portion of the data unit. In someembodiments, a same preamble format is used in the regular mode as inthe range extension mode. In one such embodiment, the preamble includesan indication set to indicate whether the regular coding scheme or therange extension coding scheme is used for at least the data portion ofthe data unit. In some embodiments, the indicated regular coding schemeor range extension coding scheme is used for at least a portion of thepreamble of the data unit, in addition to the data portion of the dataunit. In an embodiment, the receiving device determines the particularcoding scheme being utilized based on the indication in the preamble ofthe data unit, and then decodes the appropriate remaining portion of thedata unit (e.g., the data portion, or a portion of the preamble and thedata portion) using the particular coding scheme.

In another embodiment, a preamble used in the range extension mode isformatted differently from a preamble used in the regular mode. Forexample, the preamble used in the range extension mode is formatted suchthat the receiving device can automatically (e.g., prior to decoding)detect that the data unit corresponds to the range extension mode. In anembodiment, when the receiving device detects that the data unitcorresponds to the range extension mode, the receiving device decodesthe data portion of the data unit, and in at least some embodiments, atleast a portion of the preamble as well as the data portion of the dataunit, using the range extension coding scheme. On the other hand, whenthe receiving device detects that the data unit does not correspond tothe range extension mode, the receiving device assumes that the dataunit corresponds to the regular mode, in an embodiment. The receivingdevice then decodes at least the data portion of the data unit using theregular coding scheme, in an embodiment.

Additionally, in at least some embodiments, a preamble of a data unit inthe regular mode and/or in the range extension mode is formatted suchthat a client station that operates according to a legacy protocol, andnot the HEW communication protocol, is able to determine certaininformation regarding the data unit, such as a duration of the dataunit, and/or that the data unit does not conform to the legacy protocol.Additionally, a preamble of the data unit is formatted such that aclient station that operates according to the HEW protocol is able todetermine the data unit conforms to the HEW communication protocol andwhether the data unit is formatted according to the regular mode or therange extension mode, in an embodiment. Similarly, a client stationconfigured to operate according to the HEW communication protocol alsotransmits data units such as described above, in an embodiment.

In at least some embodiments, data units formatted such as describedabove are useful, for example, with an AP that is configured to operatewith client stations according to a plurality of different communicationprotocols and/or with WLANs in which a plurality of client stationsoperate according to a plurality of different communication protocols.Continuing with the example above, a communication device configured tooperate according to both the HEW communication protocol (including theregular mode and the range extension mode) and a legacy communicationprotocol is able to determine that a given data unit is formattedaccording to the HEW communication protocol and not the legacycommunication protocol, and further, to determine that the data unit isformatted according to the range extension mode and not the regularmode. Similarly, a communication device configured to operate accordingto a legacy communication protocol but not the HEW communicationprotocol is able to determine that the data unit is not formattedaccording to the legacy communication protocol and/or determine aduration of the data unit.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1, the AP 14 includes other suitablenumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments. In one embodiment, the MAC processing unit 18 and thePHY processing unit 20 are configured to operate according to a firstcommunication protocol (e.g., HEW communication protocol), including atleast a first mode and a second mode of the first communicationprotocol. In some embodiments, the first mode corresponds to a rangeextension mode that uses a range extension coding scheme (e.g., blockencoding, bit-wise replication, or symbol replication), a signalmodulation scheme (e.g., phase shift keying or quadrature amplitudemodulation), or both a range extension coding scheme and signalmodulation scheme. The range extension mode is configured to increase arange and/or reduce a signal-to-noise (SNR) ratio, as compared to thesecond mode (e.g., a regular mode using a regular coding scheme), atwhich successful decoding of PHY data units conforming to the rangeextension mode is performed. In various embodiments, the range extensionmode reduces a data rate of transmission as compared to the regular modeto achieve successful decoding with increased range and/or reduced SNRratio. In another embodiment, the MAC processing unit 18 and the PHYprocessing unit 20 are also configured to operate according to a secondcommunication protocol (e.g., IEEE 802.11ac Standard). In yet anotherembodiment, the MAC processing unit 18 and the PHY processing unit 20are additionally configured to operate according to the secondcommunication protocol, a third communication protocol, and/or a fourthcommunication protocol (e.g., the IEEE 802.11a Standard and/or the IEEE802.11n Standard).

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 includes othersuitable numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the first communication protocol. In some embodiments, atleast one of the client stations 25 is not configured to operateaccording to the first communication protocol but is configured tooperate according to at least one of the second communication protocol,the third communication protocol, and/or the fourth communicationprotocol (referred to herein as a “legacy client station”).

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC processingunit 28 and a PHY processing unit 29. The PHY processing unit 29includes a plurality of transceivers 30, and the transceivers 30 arecoupled to a plurality of antennas 34. Although three transceivers 30and three antennas 34 are illustrated in FIG. 1, the client station 25-1includes other suitable numbers (e.g., 1, 2, 4, 5, etc.) of transceivers30 and antennas 34 in other embodiments.

According to an embodiment, the client station 25-4 is a legacy clientstation, i.e., the client station 25-4 is not enabled to receive andfully decode a data unit that is transmitted by the AP 14 or anotherclient station 25 according to the first communication protocol.Similarly, according to an embodiment, the legacy client station 25-4 isnot enabled to transmit data units according to the first communicationprotocol. On the other hand, the legacy client station 25-4 is enabledto receive and fully decode and transmit data units according to thesecond communication protocol, the third communication protocol, and/orthe fourth communication protocol.

In an embodiment, one or both of the client stations 25-2 and 25-3, hasa structure the same as or similar to the client station 25-1. In anembodiment, the client station 25-4 has a structure similar to theclient station 25-1. In these embodiments, the client stations 25structured the same as or similar to the client station 25-1 have thesame or a different number of transceivers and antennas. For example,the client station 25-2 has only two transceivers and two antennas (notshown), according to an embodiment.

In various embodiments, the PHY processing unit 20 of the AP 14 isconfigured to generate data units conforming to the first communicationprotocol and having formats described herein. The transceiver(s) 21is/are configured to transmit the generated data units via theantenna(s) 24. Similarly, the transceiver(s) 21 is/are configured toreceive data units via the antenna(s) 24. The PHY processing unit 20 ofthe AP 14 is configured to process received data units conforming to thefirst communication protocol and having formats described hereinafterand to determine that such data units conform to the first communicationprotocol, according to various embodiments.

In various embodiments, the PHY processing unit 29 of the client device25-1 is configured to generate data units conforming to the firstcommunication protocol and having formats described herein. Thetransceiver(s) 30 is/are configured to transmit the generated data unitsvia the antenna(s) 34. Similarly, the transceiver(s) 30 is/areconfigured to receive data units via the antenna(s) 34. The PHYprocessing unit 29 of the client device 25-1 is configured to processreceived data units conforming to the first communication protocol andhaving formats described hereinafter and to determine that such dataunits conform to the first communication protocol, according to variousembodiments.

FIG. 2A is a diagram of a prior art OFDM data unit 200 that the AP 14 isconfigured to transmit to the legacy client station 25-4 via orthogonalfrequency division multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the legacy client station 25-4 is alsoconfigured to transmit the data unit 200 to the AP 14. The data unit 200conforms to the IEEE 802.11a Standard and occupies a 20 Megahertz (MHz)band. The data unit 200 includes a preamble having a legacy shorttraining field (L-STF) 202, generally used for packet detection, initialsynchronization, and automatic gain control, etc., and a legacy longtraining field (L-LTF) 204, generally used for channel estimation andfine synchronization. The data unit 200 also includes a legacy signalfield (L-SIG) 206, used to carry certain physical layer (PHY) parameterswith the data unit 200, such as modulation type and coding rate used totransmit the data unit, for example. The data unit 200 also includes adata portion 208. FIG. 2B is a diagram of example data portion 208 (notlow density parity check encoded), which includes a service field, ascrambled physical layer service data unit (PSDU), tail bits, andpadding bits, if needed. The data unit 200 is designed for transmissionover one spatial or space-time stream in a single input single output(SISO) channel configuration.

FIG. 3 is a diagram of a prior art OFDM data unit 300 that the AP 14 isconfigured to transmit to the legacy client station 25-4 via orthogonalfrequency domain multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the legacy client station 25-4 is alsoconfigured to transmit the data unit 300 to the AP 14. The data unit 300conforms to the IEEE 802.11n Standard, occupies a 20 MHz band, and isdesigned for mixed mode situations, i.e., when the WLAN includes one ormore client stations that conform to the IEEE 802.11a Standard but notthe IEEE 802.11n Standard. The data unit 300 includes a preamble havingan L-STF 302, an L-LTF 304, an L-SIG 306, a high throughput signal field(HT-SIG) 308, a high throughput short training field (HT-STF) 310, and Mdata high throughput long training fields (HT-LTFs) 312, where M is aninteger generally determined by the number of spatial streams used totransmit the data unit 300 in a multiple input multiple output (MIMO)channel configuration. In particular, according to the IEEE 802.11nStandard, the data unit 300 includes two HT-LTFs 312 if the data unit300 is transmitted using two spatial streams, and four HT-LTFs 312 isthe data unit 300 is transmitted using three or four spatial streams. Anindication of the particular number of spatial streams being utilized isincluded in the HT-SIG field 308. The data unit 300 also includes a dataportion 314.

FIG. 4 is a diagram of a prior art OFDM data unit 400 that the AP 14 isconfigured to transmit to the legacy client station 25-4 via orthogonalfrequency domain multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the legacy client station 25-4 is alsoconfigured to transmit the data unit 400 to the AP 14. The data unit 400conforms to the IEEE 802.11n Standard, occupies a 20 MHz band, and isdesigned for “Greenfield” situations, i.e., when the WLAN does notinclude any client stations that conform to the IEEE 802.11a Standard,and only includes client stations that conform to the IEEE 802.11nStandard. The data unit 400 includes a preamble having a high throughputGreenfield short training field (HT-GF-STF) 402, a first high throughputlong training field (HT-LTF1) 404, a HT-SIG 406, and M data HT-LTFs 408,where M is an integer which generally corresponds to a number of spatialstreams used to transmit the data unit 400 in a multiple input multipleoutput (MIMO) channel configuration. The data unit 400 also includes adata portion 410.

FIG. 5 is a diagram of a prior art OFDM data unit 500 that the AP 14 isconfigured to transmit to the legacy client station 25-4 via orthogonalfrequency domain multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the legacy client station 25-4 is alsoconfigured to transmit the data unit 500 to the AP 14. The data unit 500conforms to the IEEE 802.11ac Standard and is designed for “Mixed field”situations. The data unit 500 occupies a 20 MHz bandwidth. In otherembodiments or scenarios, a data unit similar to the data unit 500occupies a different bandwidth, such as a 40 MHz, an 80 MHz, or a 160MHz bandwidth. The data unit 500 includes a preamble having an L-STF502, an L-LTF 504, an L-SIG 506, two first very high throughput signalfields (VHT-SIGAs) 508 including a first very high throughput signalfield (VHT-SIGA1) 508-1 and a second very high throughput signal field(VHT-SIGA2) 508-2, a very high throughput short training field (VHT-STF)510, M very high throughput long training fields (VHT-LTFs) 512, where Mis an integer, and a second very high throughput signal field(VHT-SIG-B) 514. The data unit 500 also includes a data portion 516.

FIG. 6A is a set of diagrams illustrating modulation of the L-SIG,HT-SIG1, and HT-SIG2 fields of the data unit 300 of FIG. 3, as definedby the IEEE 802.11n Standard. The L-SIG field is modulated according tobinary phase shift keying (BPSK), whereas the HT-SIG1 and HT-SIG2 fieldsare modulated according to BPSK, but on the quadrature axis (Q-BPSK). Inother words, the modulation of the HT-SIG1 and HT-SIG2 fields is rotatedby 90 degrees as compared to the modulation of the L-SIG field.

FIG. 6B is a set of diagrams illustrating modulation of the L-SIG,VHT-SIGA1, and VHT-SIGA2 fields of the data unit 500 of FIG. 5, asdefined by the IEEE 802.11ac Standard. Unlike the HT-SIG1 field in FIG.6A, the VHT-SIGA1 field is modulated according to BPSK, same as themodulation of the L-SIG field. On the other hand, the VHT-SIGA2 field isrotated by 90 degrees as compared to the modulation of the L-SIG field.

FIG. 7A is a diagram of an OFDM data unit 700 that the AP 14 isconfigured to transmit to the client station 25-1 via orthogonalfrequency domain multiplexing (OFDM) modulation, according to anembodiment. In an embodiment, the client station 25-1 is also configuredto transmit the data unit 700 to the AP 14. The data unit 700 conformsto the first communication protocol and occupies a 20 MHz bandwidth.Data units that conform to the first communication protocol similar tothe data unit 700 may occupy other suitable bandwidth such as 40 MHz, 80MHz, 160 MHz, 320 MHz, 640 MHz, for example, or other suitablebandwidths, in other embodiments. The data unit 700 is suitable for“mixed mode” situations, i.e., when the WLAN 10 includes a clientstation (e.g., the legacy client station 25-4) that conforms to a legacycommunication protocol, but not the first communication protocol. Thedata unit 700 is utilized in other situations as well, in someembodiments.

In an embodiment, the data unit 700 includes a preamble 701 having anL-STF 702, an L-LTF 704, an L-SIG 706, two first HEW signal fields(HEW-SIGAs) 708 including a first HEW signal field (HEW-SIGA1) 708-1 anda second HEW signal field (HEW-SIGA2) 708-2, an HEW short training field(HEW-STF) 710, M HEW long training fields (HEW-LTFs) 712, where M is aninteger, and a third HEW signal field (HEW-SIGB) 714. Each of the L-STF702, the L-LTF 704, the L-SIG 706, the HEW-SIGAs 708, the HEW-STF 710,the M HEW-LTFs 712, and the HEW-SIGB 714 comprises an integer number ofone or more OFDM symbols. For example, in an embodiment, the HEW-SIGAs708 comprise two OFDM symbols, where the HEW-SIGA1 708-1 field comprisesthe first OFDM symbol and the HEW-SIGA2 comprises the second OFDMsymbol. In another embodiment, for example, the preamble 701 includes athird HEW signal field (HEW-SIGA3, not shown) and the HEW-SIGAs 708comprise three OFDM symbols, where the HEW-SIGA1 708-1 field comprisesthe first OFDM symbol, the HEW-SIGA2 comprises the second OFDM symbol,and the HEW-SIGA3 comprises the third OFDM symbol. In at least someexamples, the HEW-SIGAs 708 are collectively referred to as a single HEWsignal field (HEW-SIGA) 708. In some embodiments, the data unit 700 alsoincludes a data portion 716. In other embodiments, the data unit 700omits the data portion 716.

In the embodiment of FIG. 7A, the data unit 700 includes one of each ofthe L-STF 702, the L-LTF 704, the L-SIG 706, the HEW-SIGA1s 708. Inother embodiments in which an OFDM data unit similar to the data unit700 occupies a cumulative bandwidth other than 20 MHz, each of the L-STF702, the L-LTF 704, the L-SIG 706, the HEW-SIGA1s 708 is repeated over acorresponding number of 20 MHz sub-bands of the whole bandwidth of thedata unit, in an embodiment. For example, in an embodiment, the OFDMdata unit occupies an 80 MHz bandwidth and, accordingly, includes fourof each of the L-STF 702, the L-LTF 704, the L-SIG 706, the HEW-SIGA1s708, in an embodiment. In some embodiments, the modulation of different20 MHz sub-bands signals is rotated by different angles. For example, inone embodiment, a first sub-band is rotated 0-degrees, a second sub-bandis rotated 90-degrees, a third sub-band is rotated 180-degrees, and afourth sub-band is rotated 270-degrees. In other embodiments, differentsuitable rotations are utilized. The different phases of the 20 MHzsub-band signals result in reduced peak to average power ratio (PAPR) ofOFDM symbols in the data unit 700, in at least some embodiments. In anembodiment, if the data unit that conforms to the first communicationprotocol is an OFDM data unit that occupies a cumulative bandwidth suchas 20 MHz, 40 MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz, etc., the HEW-STF,the HEW-LTFs, the HEW-SIGB and the HEW data portion occupy thecorresponding whole bandwidth of the data unit.

FIG. 7B is a set of diagrams illustrating modulation of the L-SIG 706,HEW-SIGA1 708-1, and HEW-SIGA2 708-2 of the data unit 700 of FIG. 7A,according to an embodiment. In this embodiment, the L-SIG 706, HEW-SIGA1708-1, and HEW-SIGA2 708-2 fields have the same modulation as themodulation of the corresponding field as defined in the IEEE 802.11acStandard and depicted in FIG. 6B. Accordingly, the HEW-SIGA1 field ismodulated the same as the L-SIG field. On the other hand, the HEW-SIGA2field is rotated by 90 degrees as compared to the modulation of theL-SIG field. In some embodiments having the third HEW-SIGA3 field, theHEW-SIGA2 field is modulated the same as the L-SIG field and theHEW-SIGA1 field, while the HEW-SIGA3 field is rotated by 90 degrees ascompared to the modulation of the L-SIG field, the HEW-SIGA1 field, andthe HEW-SIGA2 field.

In an embodiment, because the modulations of the L-SIG 706, HEW-SIGA1708-1, and HEW-SIGA2 708-2 fields of the data unit 700 correspond to themodulations of the corresponding fields in a data unit that conforms tothe IEEE 802.11ac Standard (e.g., the data unit 500 of FIG. 5), legacyclient stations configured to operate according to the IEEE 802.11aStandard and/or the IEEE 802.11n Standard will assume, in at least somecircumstances, that the data unit 700 conforms to the IEEE 802.11acStandard and will process the data unit 700 accordingly. For example, aclient station that conforms to the IEEE 802.11a Standard will recognizethe legacy IEEE 802.11a Standard portion of the preamble of the dataunit 700 and will set a duration of the data unit (or the data unitduration) according to a duration indicated in the L-SIG 706. Forexample, the legacy client station 25-4 will calculate a duration forthe data unit based on a rate and a length (e.g., in number of bytes)indicated in the L-SIG field 706, according to an embodiment. In anembodiment, the rate and the length in the L-SIG field 706 are set suchthat a client station configured to operate according to a legacycommunication protocol will calculate, based the rate and the length, apacket duration (T) that corresponds to, or at least approximates, theactual duration of the data unit 700. For example, the rate is set toindicate a lowest rate defined by the IEEE 802.11a Standard (i.e., 6Mbps), and the length is set to a value computed such that packetduration computed using the lowest rate at least approximates the actualduration of the data unit 700, in one embodiment.

In an embodiment, a legacy client station that conforms to the IEEE802.11a Standard, when receiving the data unit 700, will compute apacket duration for the data unit 700, e.g., using a rate field and alength field of L-SIG field 706, and will wait until the end of thecomputed packet duration before performing clear channel assessment(CCA), in an embodiment. Thus, in this embodiment, communication mediumis protected against access by the legacy client station at least forthe duration of the data unit 700. In an embodiment, the legacy clientstation will continue decoding the data unit 700, but will fail an errorcheck (e.g., using a frame check sequence (FCS)) at the end of the dataunit 700.

Similarly, a legacy client station configured to operate according tothe IEEE 802.11n Standard, when receiving the data unit 700, willcompute a packet duration (T) of the data unit 700 based on the rate andthe length indicated in the L-SIG 706 of the data unit 700, in anembodiment. The legacy client station will detect the modulation of thefirst HEW signal field (HEW-SIGA1) 708-1 (BPSK) and will assume that thedata unit 700 is a legacy data unit that conforms to the IEEE 802.11aStandard. In an embodiment, the legacy client station will continuedecoding the data unit 700, but will fail an error check (e.g., using aframe check sequence (FCS)) at the end of the data unit. In any event,according to the IEEE 802.11n Standard, the legacy client station willwait until the end of a computed packet duration (T) before performingclear channel assessment (CCA), in an embodiment. Thus, communicationmedium will be protected from access by the legacy client station forthe duration of the data unit 700, in an embedment.

A legacy client station configured to operate according to the IEEE802.11ac Standard but not the first communication protocol, whenreceiving the data unit 700, will compute a packet duration (T) of thedata unit 700 based on the rate and the length indicated in the L-SIG706 of the data unit 700, in an embodiment. However, the legacy clientstation will not be able to detect, based on the modulation of the dataunit 700, that the data unit 700 does not conform to the IEEE 802.11acStandard, in an embodiment. In some embodiments, one or more HEW signalfields (e.g., the HEW-SIGA1 and/or the HEW-SIGA2) of the data unit 700is/are formatted to intentionally cause the legacy client station todetect an error when decoding the data unit 700, and to therefore stopdecoding (or “drop”) the data unit 700. For example, HEW-SIGA 708 of thedata unit 700 is formatted to intentionally cause an error when the SIGAfield is decoded by a legacy device according to the IEEE 802.11acStandard, in an embodiment. Further, according to the IEEE 802.11acStandard, when an error is detected in decoding the VHT-SIGA field, theclient station will drop the data unit 700 and will wait until the endof a computed packet duration (T), calculated, for example, based on arate and a length indicated in the L-SIG 706 of the data unit 700,before performing clear channel assessment (CCA), in an embodiment.Thus, communication medium will be protected from access by the legacyclient station for the duration of the data unit 700, in an embodiment.

FIG. 8 is a diagram of an OFDM symbol 800, according to an embodiment.The data unit 700 of FIG. 7 includes OFDM symbols such as the OFDMsymbols 800, in an embodiment. The OFDM symbol 800 includes a guardinterval (GI) portion 802 and an information portion 804. In anembodiment, the guard interval comprises a cyclic prefix repeating anend portion of the OFDM symbol. In an embodiment, the guard intervalportion 802 is used to ensure orthogonality of OFDM tones at a receivingdevice (e.g., the client station 25-1) and to minimize or eliminateinter-symbol interference due to multi-path propagation in thecommunication channel via which the OFDM symbol 800 is transmitted froma transmitting device (e.g., the AP 14) to the receiving device. In anembodiment, the length of the guard interval portion 802 is selectedbased on expected worst case channel delay spread in the communicationchannel between the transmitting device and the receiving device. Forexample, a longer guard interval is selected for outdoor communicationchannels typically characterized by longer channel delay spreads ascompared to a shorter guard interval selected for indoor communicationchannels typically characterized by shorter channel delay spreads, in anembodiment. In an embodiment, the length of the guard interval portion802 is selected based on a tone spacing (e.g., spacing betweensub-carrier frequencies of the whole bandwidth of the data unit) withwhich the information portion 804 has been generated. For example, alonger guard interval is selected for a narrower tone spacing (e.g., 256tones) as compared to a shorter guard interval for a wider tone spacing(e.g., 64 tones).

According to an embodiment, the guard interval portion 802 correspondsto a short guard interval, a normal guard interval, or a long guardinterval, depending on mode of transmission being utilized. In anembodiment, the short guard interval or the normal guard interval isused for indoor communication channels, communication channels withrelatively short channel delay spreads, or communication channels havingsuitably high SNR ratios, and the long guard interval is used foroutdoor communication channels, communication channels with relativelylong delay spreads, or communication channels not having suitably highSNR ratios. In an embodiment, the normal guard interval or the shortguard interval is used for some or all OFDM symbols of an HEW data unit(e.g., the HEW data unit 700) when the HEW data unit is transmitted inthe regular mode, and the long guard interval is used for at least someOFDM symbols of the HEW data unit when the HEW data unit is transmittedin the range extension mode.

In an embodiment, the short guard interval (SGI) has a length of 0.4 μs,the normal guard interval is 0.8 μs and the long guard interval (LGI)has a length of 1.2 μs or 1.8 μs. In an embodiment, the informationportion 804 has a length of 3.2 μs. In other embodiments, theinformation portion 804 has an increased length that corresponds to thetone spacing with which the information portion 804 has been generated.For example, the information portion 804 has a first length of 3.2 μsfor the regular mode using a first tone spacing of 64 tones and has asecond length of 6.4 μs for a second tone spacing of 128 tones, wherethe second tone spacing and second length are both increased by aninteger multiple of 2 as compared to the first tone spacing and firstlength. In an embodiment, the remaining length of the informationportion 804 is filled with a copy of a received time-domain signal(e.g., the information portion 804 contains two copies of the receivedtime-domain signal). In other embodiments, other suitable lengths forthe SGI, the NGI, the LGI, and/or the information portion 804 areutilized. In some embodiments, the SGI has a length that is 50% of thelength of the NGI, and the NGI has a length that is 50% of the length ofthe LGI. In other embodiments, the SGI has a length that is 75% or lessof the length of the NGI, and the NGI has a length that is 75% or lessof the length of the LGI. In other embodiments, the SGI has a lengththat is 50% or less of the length of the NGI, and the NGI has a lengththat is 50% or less of the LGI.

In other embodiments, OFDM modulation with reduced tone spacing is usedin the range extension mode using a same tone plan (e.g., apredetermined sequence of indices that indicate which OFDM tones aredesignated for data tones, pilot tones, and/or guard tones). Forexample, whereas the regular mode for a 20 MHz bandwidth OFDM data unituses a 64-point discrete Fourier transform (DFT), resulting in 64 OFDMtones (e.g., indices −32 to +31), the range extension mode uses a128-point DFT for a 20 MHz OFDM data unit, resulting in 128 OFDM tones(e.g., indices −64 to +63) in the same bandwidth. In this case, tonespacing in the range extension mode OFDM symbols is reduced by a factorof two (1/2) compared to regular mode OFDM symbols while using the sametone plan. As another example, whereas the regular mode for a 20 MHzbandwidth OFDM data unit uses a 64-point discrete Fourier transform(DFT) resulting in 64 OFDM tones, the range extension mode uses a256-point DFT for a 20 MHz OFDM data unit resulting in 256 OFDM tones inthe same bandwidth. In this case, tone spacing in the range extensionmode OFDM symbols is reduced by a factor of four (1/4) compared to theregular mode OFDM symbols. In such embodiments, long GI duration of, forexample, 1.6 μs is used. However, the duration of the informationportion of the range extension mode OFDM symbol is increased (e.g., from3.2 μs to 6.4 μs), and the percentage of the GI portion duration to thetotal OFDM symbols duration remains the same, in an embodiment. Thus, inthis case, loss of efficiency due to a longer GI symbol is avoided, inat least some embodiments. In various embodiments, the term “long guardinterval” as used herein encompasses an increased duration of a guardinterval as well as a decreased OFDM tone spacing that effectivelyincreases duration of the guard interval.

FIG. 9A is a diagram illustrating an example data unit 900 in which theregular mode or range extension mode is used for a preamble of the dataunit, according to an embodiment. The data unit 900 is generally thesame as the data unit 700 of FIG. 7A and includes like-numbered elementswith the data unit 700 of FIG. 7A. The HEW-SIGA field 708 (e.g., theHEW-SIGA1 708-1 or the HEW-SIGA2 708-2) of the data unit 900 includes acoding indication (CI) 902. According to an embodiment, the CIindication 902 is set to indicate one of (i) regular mode with a regularcoding scheme or (ii) range extension mode with a range extension codingscheme. In an embodiment, the CI indication 902 comprises one bit,wherein a first value of the bit indicates the regular mode and a secondvalue of the bit indicates the range extension mode. In someembodiments, the CI indication is combined with a modulation and codingscheme (MCS) indicator. In an embodiment, for example, the regular modecorresponds to MCS values which are determined to be valid by a legacyreceiver device (e.g., in compliance with IEEE 802.11ac protocol), whilethe range extension mode corresponds to an MCS value that is determinedto be invalid (or not supported) by the legacy receiver device (e.g.,not in compliance with IEEE 802.11ac protocol). In other embodiments,the CI indication 902 has a plurality of bits that indicate a pluralityof regular mode MCS values and a plurality of range extension mode MCSvalues. As illustrated in FIG. 9A, the regular coding scheme is used forall OFDM symbols of the preamble of the data unit 700, and one of theregular coding scheme or the range extension coding scheme, as indicatedby the CI indication 902, is used for OFDM symbols of the data portion716, in the illustrated embodiment.

In an embodiment, for example, where the range extension coding schemeis used for OFDM symbols of the data portion 716, the range and/or SNRat which successful decoding of PHY data units is generally improved(i.e., successful decoding at longer range and/or lower SNR) as comparedto regular data units. In some embodiments, the improved range and/orSNR performance is not necessarily achieved for decoding of the preamble701, which is generated using the regular coding scheme. In suchembodiments, transmission of at least a portion of the preamble 701 witha transmission power boost, as compared to transmission power used fortransmission of the data portion 716, to increase a decoding range ofthe portion of the preamble 701. In some embodiments, the portion of thepreamble 701 that is transmitted with the transmission power boostincludes legacy fields, such as the L-STF 702, L-LTF 704, and L-SIG 708,and/or non-legacy fields, such as the HEW-STF and HEW-LTF. In variousembodiments, the transmission power boost is 3 dB, 6 dB, or othersuitable values. In some embodiments, the transmission power boost isdetermined such that the “boosted” preamble 701 is decodable withsimilar performance as compared to the “unboosted” data portion 716 at asame location. In some embodiments, an increased length of the L-STF702, L-LTF 704, and/or L-SIG 706 is used in combination with thetransmission power boost. In other embodiments, the increased length ofthe L-STF 702, L-LTF 704, and/or L-SIG 706 is used instead of thetransmission power boost.

FIG. 9B is a diagram illustrating an example data unit 950 in which therange extension coding scheme is used for a portion of a preamble of thedata unit, according to an embodiment. The data unit 950 is generallythe same as the data unit 900 of FIG. 9A, except that in the data unit950 includes a preamble 751 in which the coding scheme indicated by theCI indication 902 is applied to OFDM symbols of a portion of thepreamble 751 as well as to the OFDM symbols of the data portion 716. Inparticular, in the illustrated embodiment, the regular coding scheme isused for a first portion 751-1 of the preamble 701, and one of theregular coding scheme or the range extension coding scheme, as indicatedby the CI indication 902, is used for OFDM symbols of a second portion751-2 of the preamble 751, in addition to OFDM symbols of the dataportion 716. Accordingly, the coding scheme indicated by the CIindication 902 skips the OFDM symbol that corresponds to the HEW-STF 710and is applied beginning with the OFDM symbol that corresponds to theHEW-LTF 712-1, in the illustrated embodiment. Skipping the HEW-STF 710allows the device receiving the data unit 950 sufficient time to decodethe CI indication 902 and to properly set up the receiver to begindecoding OFDM symbols using the coding scheme indicated by the CIindication 902 prior to receiving such OFDM symbols, in at least someembodiments.

FIG. 10A is a diagram illustrating an example data unit 1000 in whichOFDM tone spacing adjustment is used in combination with bit and/orsymbol repetition for the range extension coding scheme, according to anembodiment. The data unit 1000 is generally the same as the data unit900 of FIG. 7A, except that in the data unit 1000, when the CIindication 902 indicates that the range extension coding scheme is beingutilized, the OFDM symbols of the data portion 716 are generated usingOFDM modulation with reduced tone spacing compared to tone spacing usedfor regular mode OFDM symbols of the data unit 1000.

FIG. 10B is a diagram illustrating an example data unit 1050 in whichOFDM tone spacing adjustment is used in combination with bit and/orsymbol repetition for the range extension coding scheme, according toanother embodiment. The data unit 1050 is generally the same as the dataunit 950 of FIG. 9B, except that in the data unit 1050, when the CIindication 902 indicates that the range extension coding scheme is beingutilized, the OFDM symbols of the second portion 751-2 and OFDM symbolsof the data portion 716 are generated using OFDM modulation with reducedtone spacing compared to tone spacing used for regular mode OFDM symbolsof the data unit 1050. In the embodiment shown in FIG. 10A, an overallbandwidth of 20 MHz is used with normal tone spacing and guard intervalin the first portion 751-1 and tone spacing reduced by 2, long guardinterval, and an FFT size of 64 repeated twice across the overallbandwidth. In some embodiments, a transmission power boost is applied tothe first portion 751-1. In other embodiments, other multiples such as4×, 8×, or other suitable values are used for one or more of reducedtone spacing, increased guard interval, increased symbol duration, orincreased repetition across overall bandwidth.

In some embodiments, a different preamble format is used for rangeextension mode data units compared to the preamble used for regular modedata units. In such embodiments, a device receiving a data unit canautomatically detect whether the data unit is a regular mode data unitor a range extension mode data unit based on the format of the preambleof the data unit. FIG. 11A is a diagram illustrating a regular mode dataunit 1100, according to an embodiment. The regular mode data unit 1100includes a regular mode preamble 1101. The regular mode preamble 1101 isgenerally the same as the preamble 701 of the data unit 700 of FIG. 7A.In an embodiment, the preamble 1101 includes a HEW-SIGA field 1108,which includes a first HEW-SIGA1 field 1108-1 and a second firstHEW-SIGA2 field 1108-1. In an embodiment, the HEW-SIGA field 1108 (e.g.,the HEW-SIGA1 1108-1 or the HEW-SIGA2 1108-2) of the preamble 1101includes a CI indication 1102. The CI indication 1102 is set to indicatewhether the range extension coding scheme or the regular coding schemeis used for OFDM symbols of the data portion 716 of the data unit 1100,in an embodiment. In an embodiment, the CI indication 1102 comprises onebit, wherein a first value of the bit indicates the regular codingscheme and a second value of the bit indicates the range extensioncoding scheme. As will be explained in more detail below, a devicereceiving the data unit 1100 is able to detect, based on the format ofthe preamble 1101, that the preamble 1101 is a regular mode preamble,and not an extension mode preamble, in an embodiment. Upon detectingthat the preamble 1101 is the regular mode preamble, the receivingdevice determines, based on the CI indication 1102, whether the rangeextension coding scheme or the regular coding scheme is used for OFDMsymbols of the data portion 716, and decodes the data portion 716accordingly, in an embodiment. In some embodiments, when the CIindication 1102 indicates that the range extension coding scheme isbeing utilized, the OFDM symbols of a portion of the preamble 1101(e.g., the HEW-LTFs and HEW-SIGB, as and OFDM symbols of the dataportion 716 are generated using OFDM modulation with smaller tonespacing compared to tone spacing used for regular mode OFDM symbols ofthe data unit 1050

FIG. 11B is a diagram illustrating a range extension mode data unit1150, according to an embodiment. The range extension mode data unit1150 includes a range extension mode preamble 1151. The data unit 1150is generally similar to the data unit 1100 of FIG. 11A, except that thepreamble 1151 of the data unit 1150 is formatted differently from thepreamble 1101 of the data unit 1100. In an embodiment, the preamble 1151is formatted such that a receiving device that operates according to theHEW communication protocol is able to determine that the preamble 1151is a range extension mode preamble rather than a regular mode preamble.In an embodiment, the range extension mode preamble 1151 includes anL-STF 702, an L-LTF 704, and an L-SIG 706, and one or more first HEWsignal fields (HEW-SIGAs) 1152. In an embodiment, the preamble 1150further includes one or more secondary L-SIG(s) 1154 that follow theL-SIG field 706. The secondary L-SIG(s) 1154 are followed by a secondL-LTF field (L-LTF2) 1156, in some embodiments. In other embodiments,the preamble 1151 omits the L-SIG(s) 1154 and/or the L-LTF2 1156. Insome embodiments, the preamble 1151 also includes an HEW-STF 1158, oneor more HEW-LTF fields 1160, and a second HEW signal field (HEW-SIGB)1162. In other embodiments, the preamble 1151 omits the HEW-STF 1158,the HEW-LTF(s) 1160 and/or the HEW-SIGB 1162. In an embodiment, the dataunit 1150 also includes a data portion 716 (not shown in FIG. 11B). Insome embodiments, the HEW signal fields (HEW-SIGAs) 1152 are modulatedusing a same range extension coding scheme as the data field 716.

In an embodiment, one or more symbols of the HEW-SIGAs 1152 is modulatedusing QBPSK instead of BPSK, for example, to allow autodetection betweenthe regular mode and the range extension mode by the receiving devicethat operates according to the HEW communication protocol. In anembodiment, for example, where the regular mode preamble includes twoBPSK symbols and one Q-BPSK symbol after the L-SIG 706 field, the rangeextension mode preamble includes three BPSK symbols and one Q-BPSKsymbol after the L-SIG 706 field. In an embodiment, for example, whenusing a 4× bit-wise repetition of MCSO with 48 data tones in each 64-FFT(20 MHz). In some embodiments, for example, where autodetectiondifferentiate the regular mode from the range extension mode, some bitsare omitted from the HEW-SIGAs 1152, such as bits used to indicatesignal bandwidth, MCS value, or other suitable bits.

In one embodiment in which the preamble 1151 includes one or moresecondary L-SIG(s) 1154, the content of each of the L-SIG(s) 1154 is thesame as the content of the L-SIG 706 of the data unit 1150. In anembodiment, a receiving device receiving the data unit 1150 determinesthat the preamble 1151 corresponds to a range extension mode preamble bydetecting the repetition(s) of the L-SIG fields 706, 1154. Further, inan embodiment, both a rate subfield and a length subfield of the L-SIG706, and, accordingly, the rate subfield(s) and the length subfield(s)of the secondary L-SIG(s) 1154 are set to fixed (e.g., predetermined)values. In this case, upon detecting the repetition(s) of the L-SIGfields 706, 1154, the receiving device uses the fixed values in therepeating L-SIG fields as additional training information to improvechannel estimation, in an embodiment. In some embodiments, however, atleast the length subfield of the L-SIG 706, and accordingly at least thelength fields of the secondary L-SIG(s) 1154, is not set to a fixedvalue. For example, the length field is instead set to a valuedetermined based on the actual length of the data unit 1150, in anembodiment. In one such embodiment, the receiving device first decodesthe L-SIG 706, and then detects the repetition(s) of the L-SIG fields706, 1154 using the value of the length subfield in L-SIG 706. Inanother embodiment, the receiving device first detects the repetition(s)of the L-SIG fields 706, 1154, and then combines the detected multipleL-SIG fields 706, 1154 to improve decoding reliability of the L-SIGfields 706, 1154 and/or uses the redundant information in the multipleL-SIG fields 706, 1154 to improve channel estimation.

In an embodiment in which the preamble 1151 includes L-LTF2 1156, theOFDM symbol(s) of the L-LTF2 1156 are generated using the rangeextension coding scheme. In another embodiment in which the preamble1151 includes L-LTF2 11156, the OFDM symbol(s) of the L-LTF2 1156 aregenerated using the regular coding scheme. For example, if a doubleguard interval (DGI) used in the L-LTF 704 is sufficiently long for thecommunication channel in which the data unit 1150 travels from thetransmitting device to the receiving device, then OFDM symbols of theL-LTF2 1156 are generated using the regular coding scheme or,alternatively, the preamble 1151 omits the L-LTF2 1156, in anembodiment.

In another embodiment, the preamble 1151 omits the secondary L-SIG(s)1154, but includes the L-LTF2 1156. In this embodiment, a receivingdevice detects that the preamble 1151 is the range extension modepreamble by detecting the presence of the L-LTF2 1156. FIGS. 12A-12B arediagrams illustrating two possible formats of LTFs suitable for use asthe L-LTF2 1156 according to two example embodiments. Turning first toFIG. 12A, in a first example embodiment, an L-LTF2 1200 is formatted inthe same manner as the L-LTF 704, i.e., as defined by a legacycommunication protocol (e.g., the IEEE 802.11a/n/ac Standards). Inparticular, in the illustrated embodiment, the L-LTF2 1200 includes adouble guard interval (DGI) 1202 followed by two repetitions of a longtraining sequence 1204, 1206. Turning now to FIG. 12B, in anotherexample embodiment, an L-LTF2 1208 is formatted differently from theL-LTF 704. In particular, in the illustrated embodiment, the L-LTF2 1208includes a first normal guard interval 1210, a first repetition of along training sequence 1212, a second normal guard interval 1214, and asecond repetition of the long training sequence 1216.

Referring back to FIG. 11B, in an embodiment, the HEW-SIGA(s) 1152 aregenerated using the range extension coding scheme. In an embodiment, thenumber of the HEW-SIGAs 1152 is the same as the number of theHEW-SIGA(s) 1108 of the regular mode preamble 1101. Similarly, in anembodiment, the content of the HEW-SIGAs 1152 is the same as the contentof the HEW-SIGA(s) 1108 of the regular mode preamble 1101. In otherembodiments, the number and/or the content of the HEW-SIGAs 1152 isdifferent from the number and/or content of the HEW-SIGA(s) 1108 of theregular mode preamble 1101. A device receiving the data unit 1150decodes the HEW-SIGA(s) 1152 using the range extension coding schemebased on detecting that the preamble 1151 corresponds to the rangeextension mode preamble and interprets the HEW-SIGA(s) 1152appropriately as defined for the range extension mode, in an embodiment.

In an embodiment in which the preamble 1151 omits the L-SIG(s) 1154and/or L-LTF2 1156, a receiving device determines whether a preamblecorresponds to the range extension mode preamble 1151 or to the normalmode preamble 1101 by detecting whether the HEW-SIGA field in thepreamble is generated using the range extension coding scheme or theregular coding scheme based on auto-correlation of the HEW-SIGA fieldusing the range extension coding scheme and the regular coding scheme.FIGS. 13A-13B are diagrams of the HEW-SIGA 1108 of the regular modepreamble 1101 and the HEW-SIGA 1152 of the range extension mode preamble1151, respectively, according to an embodiment. In the illustratedembodiment, the HEW-SIGA 1108 of the regular mode preamble 1101 includesa first NGI 1302, a first HEW-SIGA field 1304, a second NGI 1306, and asecond HEW-SIGA field 1308. On the other hand, the HEW-SIGA 1152 of therange extension mode preamble 1151 includes a first LGI 1310, a firstHEW-SIGA field 1312, a second LGI 1314, and a second HEW-SIGA field1312. In an embodiment, a receiving device performs a firstauto-correlation of the HEW-SIGA field using a normal guard intervalstructure, such as the structure illustrated in FIG. 13A, performs asecond auto-correlation using a long guard interval structure, such asthe structure illustrated in FIG. 13B, and performs a comparison of theauto-correlation results. If auto-correlation of the HEW-SIGA fieldusing the long guard interval produces a greater result compared to theresult of the auto-correlation of the HEW-SIGA field using the normalguard interval, then the receiving device determines that the preamblecorresponds to the range extension mode preamble 1151, in an embodiment.On the other hand, if auto-correlation of the HEW-SIGA field using thenormal guard interval produces a greater result compared to the resultof auto-correlation of the HEW-SIGA field with the long guard interval,then the receiving device determines that the preamble corresponds tothe regular mode preamble 1101, in an embodiment.

Referring again to FIG. 11B, in an embodiment, the preamble 1151 isformatted such that a legacy client station can determine a duration ofthe data unit 1150 and/or that the data unit does not conform to alegacy communication protocol. Additionally, the preamble 1151 isformatted such that a client station that operates according to the HEWprotocol is able to determine that the data unit conforms to the HEWcommunication protocol, in an embodiment. For example, at least two OFDMsymbols immediately following the L-SIG 706 of the preamble 1151, suchas the L-SIG(s) 1154 and/or the L-LTF2 1156 and/or the HEW-SIGA(s) 1152,are modulated using BPSK modulation. In this case, a legacy clientstation will treat the data unit 1150 as a legacy data unit, willdetermine a duration of the data unit based on the L-SIG 706, and willrefrain from accessing the medium for the determined duration, in anembodiment. Further, one or more other OFDM symbols of the preamble1151, such as one or more of the HEW-SIG(s) 1152 are modulated usingQ-BPSK modulation, allowing a client station operating according to theHEW communication protocol to detect that the data unit 1150 conforms tothe HEW communication protocol, in an embodiment.

In some embodiments, the HEW communication protocol allows beamformingand/or multi user MIMO (MU-MIMO) transmission in the range extensionmode. In other embodiments, the HEW communication protocol allows onlysingle stream and/or only single user transmission in the rangeextension mode. With continued reference to FIG. 11B, in an embodimentin which the preamble 1151 includes the HEW-STF 1158 and the HEW-LTF(s)1160, the AP 14 applies beamforming and/or multi-user transmissionbeginning with the HEW-STF 1158. In other words, the fields of thepreamble 1151 precede the HEW-STF 1158 are omni-directional and, inmulti-user mode, are intended to be received by all intended recipientsof the data unit 1150, while the HEW-STF field 1158, as well as thepreamble fields that follow the HEW-STF field 1158 and the data portionthat follows the preamble 1151, are beam-formed and/or include differentportions intended to be received by different intended recipients of thedata unit 1150, in an embodiment. In an embodiment, the HEW-SIGB field1162 includes user-specific information for the intended recipients ofthe data unit 1150 in MU-MIMO mode. The HEW-SIGB field 1162 is generatedusing the regular coding scheme or the range extension coding scheme,depending on an embodiment. Similarly, the HEW-STF 1158 is generatedusing the regular coding scheme or the range extension coding scheme,depending on an embodiment. In an embodiment, the training sequence usedon the HEW-STF 1158 is the sequence defined in a legacy communicationprotocol, such as in the IEEE 802.11ac protocol.

On the other hand, in an embodiment in which the preamble 1151 omits theHEW-STF 1158 and the HEW-LTF(s) 1160, beamforming and MUMIMO are notallowed in the extension guard interval mode. In this embodiment, onlysingle user single stream transmission is allowed in the extension guardinterval mode. In an embodiment, a receiving device obtains a singlestream channel estimate based on the L-LTF field 704, and demodulatesthe data portion of the data unit 1150 based on the channel estimateobtained based on the L-LTF field 704.

In some embodiments, a receiver device uses the HEW-STF field 1158 tore-start an automatic gain control (AGC) process for receiving the dataportion 716. The HEW-STF has a same duration as the VHT-STF (i.e., 4microseconds), in an embodiment. In other embodiments, the HEW-STF has alonger duration than the VHT-STF. In an embodiment, the HEW-STF has asame time-domain periodicity as the VHT-STF, such that in the frequencydomain there are one non-zero tones every 4 tones and using a same tonespacing as IEEE 802.11ac. In other embodiments having a 1/N tonespacing, the HEW-STF has one non-zero tone in every 4*N tones. Inembodiments where the overall bandwidth for the data unit is greaterthan 20 MHz, (e.g., 40 MHz, 80 MHz, etc.), the HEW-STF uses the samewider bandwidth VHT-STF as in IEEE 802.11ac (i.e., a duplication of the20 MHz VHT-STF for overall bandwidth of 40 MHz, 80 MHz, 160 MHz, etc.).

FIG. 14A is a block diagram illustrating a range extension mode dataunit 1400, according to an embodiment. The data unit 1400 includes arange extension mode preamble 1401. The range extension mode preamble1401 is generally similar to the range extension mode preamble 1151 ofFIG. 11B, except that the L-SIG 706 and the secondary L-SIG 1154 of thepreamble 1151 are combined into a single L-SIG field 1406 in thepreamble 1401. FIG. 14B is a diagram illustrating the L-SIG field 1406according to one embodiment. In the embodiment of FIG. 14B, the L-SIGfield 1406 includes a double guard interval 1410, a first L-SIG field1412, which includes contents of L-SIG field 706 of the preamble 1151,and a second L-SIG field 1414, which includes contents of the secondaryL-SIG2 field 1154 of the preamble 1151. In various embodiments, L-SIGfield 1406 includes a length subfield set to a fixed value or set to avariable value, as discussed above with respect to the L-SIG fields 706,1154 of FIG. 11B. In various embodiments, redundant (repeated) bits inL-SIG field 1406 are used for improved channel estimation as discussedabove with respect to L-SIG fields 706, 1154 of FIG. 11B.

In an embodiment, a legacy client station receiving the data unit 1400assumes that the L-SIG field 1406 includes a normal guard interval. Asillustrated in FIG. 14C, the FFT window for L-SIG information bitsassumed at the legacy client station is shifted compared to the actualL-SIG field 1412, in this embodiment. In an embodiment, to ensure thatconstellation points within the FFT window correspond to BPSKmodulation, as expected by the legacy client station, and thus to allowthe legacy client station to properly decode the L-SIG field 1412,modulation of the L-SIG field 1412 is phase-shifted relative to regularBPSK modulation. For example, in a 20 MHz OFDM symbol, if the normalguard interval is 0.8 μs, and the double guard interval is 1.6 μs, thenmodulation of an OFDM tone k of the L-SIG field 1412 is shifted withrespect to the corresponding OFDM tone k of the original L-SIG as can beseen from:S _(LSIG) ^((k)) =S _(SLSIG-LSIG) ^((k)) e ^(−j·2π·0.8·20/64) =S_(SLSIG-LSIG) ^((k))·(−j)  Equation 1

Accordingly, in an embodiment, L-SIG field 1412 is modulated usingreverse Q-BPSK rather than regular BPSK. Thus, for example, a bit ofvalue 1 is modulated onto −j, and a bit of value 0 is modulated onto j,resulting in {j, −j} modulation rather than the regular {1, −1} BPSKmodulation, in an embodiment. In an embodiment, due to the reverseQ-BPSK modulation of the L-SIG field 1412, a legacy client station canproperly decode the L-SIG field 1412 an determine the duration of thedata unit 1400 based on the L-SIG 1412 field, in an embodiment. A clientstation that operates according to the HEW protocol, on the other hand,can auto-detect that the preamble 1401 is a range extension modepreamble by detecting the repetition of the L-SIG field 1412 or bydetecting the reverse Q-BPSK modulation of the L-SIG field within theFFT window of the legacy client station, in an embodiment.Alternatively, in other embodiments, a client station that operatesaccording to the HEW protocol detects that the preamble 1401 is a rangeextension mode preamble using other detection methods discussed above,such as based on modulation or format of the HEW-SIGA field(s) 1152.

Referring FIGS. 11A-11B and 14A, long guard interval is used for initialOFDM symbols of both a regular mode preamble (e.g., the preamble 1101)and a range extension mode preamble (e.g., the preamble 1151 or thepreamble 1401), in some embodiments. For example, referring to Figs,11A-11B, the L-STF field 702, the L-LTF field 704 and the L-SIG field706, 1154, and HEW-SIGA field 1152 is each generated using the longguard interval, in an embodiment. Similarly, referring to FIG. 14A, theL-STF field 702, the L-LTF field 704, the L-SIG field 1406, and theHEW-SIGA(s) 1152 are generated using the long guard interval, in anembodiment. In an embodiment, a receiving device can determine whether apreamble corresponds to the regular mode preamble or the range extensionmode preamble based on modulation of the HEW-SIGA field 1152 (e.g.,Q-BPSK) or based on an indication included in the HEW-SIGA field 1152,in various embodiments. Further, similar to the preamble 1151 of FIG.11B, the preamble 1401 of FIG. 14A includes or omits the second L-LTF2field 1156, depending on the embodiment and/or scenario.

FIG. 15 is a block diagram illustrating a format of an HEW-SIGA field1500, according to an embodiment. In some embodiments, the HEW-SIGAfield(s) 1152 of the data unit 1150 or the data unit 1400 are formattedas the HEW-SIGA field 1500. In some embodiments, the HEW-SIGA field(s)1108 are formatted as the HEW-SIGA field 1500. The HEW-SIGA field 1500includes a double guard interval 1502, a first repetition of a HEW-SIGAfield 1504 and a second repetition of a HEW-SIGA field 1506. In anexample embodiment, the DGI is 1.8 μs and each repetition of HEW-SIGA is3.2 μs. In an embodiment, the repeated bits in the HEW-SIGA field 1500are used to increase reliability of decoding of the HEW-SIGA field 1500.In an embodiment, the format of the HEW-SIGA field 1500 is used toauto-detect a range extension mode preamble based on a comparisonbetween auto-correlation of the HEW-SIGA field of the preamble using theformat of the HEW-SIGA field 1500 and auto-correlation of the HEW-SIGAfield of the preamble using the regular HEW-SIGA field format used inthe regular mode, such as the format illustrated in FIG. 13A. In someembodiments, the HEW-SIGA field 1500 is modulated using less redundancyas compared to the data portion 716, because the additional time domainrepetition of the HEW-SIGA field 1500 provides a sufficient improvementin decoding performance.

FIG. 16 is a block diagram illustrating an example PHY processing unitfor generating regular mode data units using the regular coding scheme,according to an embodiment. Referring to FIG. 1, the AP 14 and theclient station 25-1, in one embodiment, each include a PHY processingunit such as the PHY processing unit 1600. In various embodiments and/orscenarios, the PHY processing unit 1600 generates range extension dataunits such as one of the data units of FIGS. 9A, 9B, 10A, or 10B, forexample. The PHY processing unit 1600 includes a scrambler 1602 thatgenerally scrambles an information bit stream to reduce the occurrenceof long sequences of ones or zeros. An FEC encoder 1606 encodesscrambled information bits to generate encoded data bits. In oneembodiment, the FEC encoder 1606 includes a binary convolutional code(BCC) encoder. In another embodiment, the FEC encoder 1606 includes abinary convolutional encoder followed by a puncturing block. In yetanother embodiment, the FEC encoder 1606 includes a low density paritycheck (LDPC) encoder. An interleaver 1610 receives the encoded data bitsand interleaves the bits (i.e., changes the order of the bits) toprevent long sequences of adjacent noisy bits from entering a decoder atthe receiver. A constellation mapper 1614 maps the interleaved sequenceof bits to constellation points corresponding to different subcarriersof an OFDM symbol. More specifically, for each spatial stream, theconstellation mapper 1614 translates every bit sequence of lengthlog₂(M) into one of M constellation points.

The output of the constellation mapper 1614 is operated on by an inversediscrete Fourier transform (IDFT) unit 1618 that converts a block ofconstellation points to a time-domain signal. In embodiments orsituations in which the PHY processing unit 1600 operates to generatedata units for transmission via multiple spatial streams, the cyclicshift diversity (CSD) unit 1622 inserts a cyclic shift into all but oneof the spatial streams to prevent unintentional beamforming. The outputof the CSD unit 1622 is provided to the guard interval (GI) insertionand windowing unit 1626 that prepends, to an OFDM symbol, a circularextension of the OFDM symbol and smooths the edges of each symbol toincrease spectral decay. The output of the GI insertion and windowingunit 1626 is provided to the analog and radio frequency (RF) unit 1630that converts the signal to analog signal and upconverts the signal toRF frequency for transmission.

In various embodiments, the range extension mode corresponds to a lowestdata rate modulation and coding scheme (MCS) of the regular mode andintroduces redundancy or repetition of bits into at least some fields ofthe data unit or repetition of symbols to further reduce the data rate.For example, the range extension mode introduces redundancy into thedata portion and/or the non-legacy signal field of a range extensionmode data unit or repetition of symbols according to one or more rangeextension coding schemes described below, in various embodiments and/orscenarios. As an example, according to an embodiment, regular mode dataunits are generated according a regular coding scheme. In variousembodiments, the regular coding scheme is a modulation and coding scheme(MCS) selected from a set of MCSs, such as MCSO (binary phase shiftkeying (BPSK) modulation and coding rate of 1/2) to MCSs (quadratureamplitude modulation (QAM) and coding rate of 5/6), with higher orderMCSs corresponding to higher data rates. Range extension mode dataunits, in one such embodiment, are generated using a range extensioncoding scheme, such as a modulation and coding as defined by MCSO andwith added bit repetition, block encoding, or symbol repetition thatfurther reduce the data rate.

FIG. 17A is a block diagram of an example PHY processing unit 1700 forgenerating range extension mode data units using a range extensioncoding scheme, according to an embodiment. In some embodiments, the PHYprocessing unit 1700 generates signal and/or data fields of rangeextension mode data units. Referring to FIG. 1, the AP 14 and the clientstation 25-1, in one embodiment, each include a PHY processing unit suchas the PHY processing unit 1700.

The PHY processing unit 1700 is similar to the PHY processing unit 1600of FIG. 16 except that the PHY processing unit 1700 includes a blockcoder 1704 coupled to a scrambler 1702. In an embodiment, the blockcoder 1704 reads incoming (scrambled) information bits one block at atime, generates a number of copies of each block (or each bit in ablock), interleaves the resulting bits according to the range extensioncoding scheme and outputs the interleaved bits for further encoding by aFEC encoder 1706 (e.g., a binary convolutional encoder). Generally, eachblock contains the number of information bits that, after having beenencoded by the block coder 1704 and by the FEC encoder 1706, fill thedata tones of a single OFDM symbol, according to an embodiment. As anexample, in one embodiment, the block coder 1704 generates two copies(2× repetition) of each block of 12 information bits to generate 24 bitsto be included in an OFDM symbol. The 24 bits are then encoded by theFEC encoder 1706 at the coding rate of 1/2 to generate 48 bits thatmodulate 48 data tones of an OFDM symbol (e.g., using BPSK modulation).As another example, in another embodiment, the block coder 1704generates four copies (4× repetition) of each block of 6 informationbits to generate 24 bits which are then encoded by the FEC encoder 1706at the coding rate of 1/2 to generate 48 bits that modulate 48 datatones of an OFDM symbol. As yet another example, in another embodiment,the block coder 1704 generates two copies (2× repetition) of each blockof 13 information bits to generate 26 bits which are then encoded by theFEC encoder 1706 at the coding rate of 1/2 to generate 52 bits thatmodulate 52 data tones of an OFDM symbol. In other embodiments, theblock coder 1704 and FEC encoder 1706 are configured to generate 104,208, or any suitable number of bits for modulation of data tones of anOFDM symbol.

In some embodiments, the block coder 1704 applies a 4× repetition schemewhen generating a data (or a signal) field as defined by MCSO asspecified in the IEEE 802.11n Standard for 20 MHz channel, i.e., with 52data tones per OFDM symbol. In this case, according to an embodiment,the block coder 1704 generates four copies of each block of 6information bits to generate 24 bits and then adds two padding bits(i.e., two bits of a predetermined values) to provide the specifiednumber of bits (i.e., 26 bits for 52 data tones) to the BCC encoderwhich encoded the 26 bits using the coding rate of 1/2 to generate 52coded bits for modulating the 52 data tones.

In one embodiment, the block coder 1704 utilizes a “block level”repetition scheme in which each block of n bits is repeated mconsecutive times. As an example, if m is equal to 4 (4× repetitions),the block coder 1704 generates a sequence [C, C, C, C], where C is ablock of n bits, according to an embodiment. In another embodiment, theblock coder 1704 utilizes a “bit level” repetition scheme in which eachincoming bit is repeated m consecutive times. In this case, in anembodiment, if m is equal to 4 (4× repetitions), the block coder 1704generates the sequence [b1 b1 b1 b1 b2 b2 b2 b2 b3 b3 b3 b3 . . . ],where b1 is the first bit in the block of bits, b2 is the second bit,and so on. In yet another embodiment, the block coder 1704 generates mnumber of copies of the incoming bits and interleaves the resulting bitstream according to any suitable code. Alternatively, in still anotherembodiment, the block coder 1704 encodes incoming bits or incomingblocks of bits using any suitable code, e.g., a Hamming block code withthe coding rate of a 1/2, 1/4, etc., or any other block code with thecoding rate of 1/2, 1/4, etc. (e.g., (1,2) or (1, 4) block code, (12,24)block code or (6, 24) block code, a (13,26) block code, etc.).

According to an embodiment, the effective coding rate corresponding to acombination of the coding performed by the block coder 1704 and codingperformed by the FEC encoder 1706 the product of the two coding rates.For example, in an embodiment in which the block coder 1704 utilizes 4×repetition (or coding rate of 1/4) and the FEC encoder 1706 utilizes acoding rate of 1/2, the resulting effective coding rate is equal to 1/8.As a result of the reduced coding rate compared to the coding rate usedto generate a similar regular mode data unit, data rate in rangeextension mode is effectively reduced by a factor corresponding to thenumber the coding rate applied by the block coder 1704 (e.g., a factorof 2, a factor of 4, etc.), according to an embodiment.

According to some embodiments, the block coder 1704 utilizes the sameblock coding scheme for generating the signal field of a control modedata unit as the block coding scheme used for generating the dataportion of the control mode data unit. For instance, in an embodiment,an OFDM symbol of the signal field and an OFDM symbol of the dataportion each includes 48 data tones, and in this embodiment, the blockcoder 1704 applies a 2× repetition scheme to blocks of 12 bits for thesignal field and the data portion, for example. In another embodiment,the data portion and the signal field of a control mode data unit aregenerated using different block coding schemes. For example, in anembodiment, the long range communication protocol specifies a differentnumber of data tones per OFDM symbol in the signal field compared to thenumber of data tones per OFDM symbol in the data portion. Accordingly,in this embodiment, the block coder 1704 utilizes a different block sizeand, in some embodiments, a different coding scheme, when operating onthe signal field compared to the block size and the coding scheme usedfor generating the data portion. For example, if the long rangecommunication protocol specifies 52 data tones per OFDM symbol of thesignal field and 48 data tones per OFDM tones of the data portion, theblock coder 1704 applies a 2× repetition scheme to blocks of 13 bits ofthe signal field and a 2× repetition scheme to blocks of 12 bits of thedata portion, according to one embodiment.

The FEC encoder 1706 encodes the block coded information bits, accordingto an embodiment. In an embodiment, BCC encoding is performedcontinuously over the entire field being generated (e.g., the entiredata field, the entire signal field, etc.). Accordingly, in thisembodiment, information bits corresponding to the field being generatedare partitioned into blocks of a specified size (e.g., 6 bits, 12 bits,13 bits, or any other suitable number of bits), each block is processedby the block coder 1704, and the resulting data stream is then providedto the FEC encoder 1706 which continuously encodes the incoming bits.

Similar to the interleaver 1610 of FIG. 16, in various embodiments, theinterleaver 1710 changes the order of bits in order to provide diversitygain and reduce the chance that consecutive bits in a data stream willbecome corrupted in the transmission channel. In some embodiments,however, the block coder 1704 provides sufficient diversity gain and theinterleaver 1710 is omitted. In some embodiments, the interleaver 1710or the FEC encoder 1706 provides the bits to the constellation mapper1614 for transmission, as described above.

In some embodiments, information bits in the data portion of a rangeextension mode data unit are be padded (i.e., a number of bits of aknown value is added to the information bits) so that the data unitoccupies an integer number of OFDM symbols, for example. Referring toFIG. 1, in some embodiments, padding is implemented in the MACprocessing unit 18, 28 and/or the PHY processing unit 20, 29. In somesuch embodiments, the number of padding bits is determined according topadding equations provided in a short range communication protocol(e.g., the IEEE 802.11a Standard, the IEEE 802.11n Standard, the IEEE802.11ac Standard, etc.). In general, these padding equations involvecomputing a number of padding bits based, in part, on a number of databits per OFDM symbol (N_(DBPS)) and/or a number coded data bits persymbol (N_(CBPS)). In range extension mode, according to an embodiment,the number of padding bits is determined based on the number ofinformation bits in an OFDM symbol (e.g., 6 bits, 12 bits, 13bits, etc.)before the information bits are block encoded by the block coder 1704and BCC encoded by the FEC encoder 1706. Accordingly, the number ofpadding bits in a range extension mode data unit is generally differentfrom the number of padding bits in the corresponding regular mode data(or in the corresponding short range data unit). On the other hand,according to an embodiment, the number of coded bits per symbol is thesame as the number of coded bits per symbol in regular mode data unit(or in the corresponding short range data unit), e.g., 24, 48,52, etc.coded bits per OFDM.

FIG. 17B is a block diagram of an example PHY processing unit 1750 forgenerating range extension mode data units, according to anotherembodiment. In some embodiments, the PHY processing unit 1750 generatessignal and/or data fields of range extension mode data units. Referringto FIG. 1, the AP 14 and the client station 25-1, in one embodiment,each include a PHY processing unit such as the PHY processing unit 1750.

The PHY processing unit 1750 is similar to the PHY processing unit 1700of FIG. 17A, except that in the PHY processing unit 1750, the FECencoder 1706 is replaced by the LDPC encoder 1756. Accordingly, in thisembodiment, the output of the block coder 1704 is provided for furtherblock encoding by the LDPC encoder 1756. In an embodiment, the LDPCencoder 1756 utilizes a block code corresponding to a coding rate of1/2, or a block code corresponding to another suitable coding rate. Inthe illustrated embodiment, the PHY processing unit 1750 omits theinterleaver 1710 because adjacent bits in an information stream aregenerally spread out by the LDPC code itself and no further interleavingis needed. Additionally, in an embodiment, further frequency diversityis provided by the LDPC tone remapping unit 1760. According to anembodiment, the LDPC tone remapping unit 1760 reorders coded informationbits or blocks of coded information bits according to a tone remappingfunction. The tone remapping function is generally defined such thatconsecutive coded information bits or blocks of information bits aremapped onto nonconsecutive tones in the OFDM symbol to facilitate datarecovery at the receiver in cases in which consecutive OFDM tones areadversely affected during transmission. In some embodiments, the LDPCtone remapping unit 1760 is omitted. Referring again to FIG. 17A, invarious embodiments, a number of tail bits are typically added to eachfield of a data unit for proper operation of the FEC encoder 1706, e.g.,to ensure that the BCC encoder, after having encoded each field, isbrought back to zero state. In one embodiment, for example, six tailbits are inserted at the end of the data portion before the data portionis provided to the FEC encoder 1706 (e.g., after the bits are processedby the block coder 1704).

In some embodiments, the signal field of a range extension mode dataunit has a different format compared to the signal field format of aregular mode data unit. In some such embodiment, the signal field ofrange extension mode data units is shorter compared to a signal field ofa regular mode data unit. For example, only one modulation and codingscheme is used in range extension mode, according to an embodiment, andtherefore less information (or no information) regarding modulation andcoding needs to be communicated in the range extension mode signalfield. Similarly, in an embodiment, maximum length of a range extensionmode data unit is shorter compared to a maximum length of a regular modedata unit and, in this case, less bits are needed for the lengthsubfield of the range extension mode signal field. As an example, in oneembodiment, a range extension mode signal field is formatted accordingto the IEEE 802.11n Standard but omits certain subfields (e.g., the lowdensity parity check (LDPC) subfield, the space time block coding (STBC)subfield, etc.). Additionally or alternatively, in some embodiments, arange extension mode signal field includes a shorter CRC subfieldcompared to the cyclic redundancy check (CRC) subfield of a regular modesignal field (e.g., less than 8 bits). In general, in range extensionmode, certain signal field subfields are omitted or modified and/orcertain new information is added, according to some embodiments.

FIG. 18A is a block diagram of an example PHY processing unit 1800 forgenerating range extension mode data units using a range extensioncoding scheme, according to another embodiment. In some embodiments, thePHY processing unit 1800 generates signal and/or data fields of rangeextension mode data units. Referring to FIG. 1, the AP 14 and the clientstation 25-1, in one embodiment, each include a PHY processing unit suchas the PHY processing unit 1800.

The PHY processing unit 1800 is similar to the PHY processing unit 1700of FIG. 17A, except that in the PHY processing unit 1800 a block coder1808 is located after an FEC encoder 1806. Accordingly, in thisembodiment, information bits are first scrambled by scrambler 1802,encoded by the FEC encoder 1806 and the FEC coded bits are thenreplicated or otherwise block encoded by the block coder 1808. As in theexample embodiment of the PHY processing unit 1700, in an embodiment,processing by the FEC encoder 1806 is performed continuously over theentire field being generated (e.g., the entire data portion, the entiresignal field, etc.). Accordingly, in this embodiment, information bitscorresponding to the field being generated are first encoded by the FECencoder 1806 and the BCC coded bits are then partitioned into blocks ofa specified size (e.g., 6 bits, 12 bits, 13 bits, or any other suitablenumber of bits). Each block is then processed by the block coder 1808.As an example, in one embodiment, the FEC encoder 1806 encodes 12information bits per OFDM symbol using the coding rate of 1/2 togenerate 24 BCC coded bits and provides the BCC coded bits to the blockcoder 1808. In an embodiment, the block coder 1808 generates two copiesof each incoming block and interleaves the generated bits according to arange extension coding scheme coding scheme to generate 48 bits to beincluded in an OFDM symbol. In one such embodiment, the 48 bitscorrespond to 48 data tones generated using a Fast Fourier Transform(FFT) of size 64 at the IDFT processing unit 1818. As another example,in another embodiment, the FEC encoder 1806 encodes 6 information bitsper OFDM symbol using the coding rate of 1/2 to generate 12 BCC codedbits and provides the BCC coded bits to the block coder 1808. In anembodiment, the block coder 1808 generates two copies of each incomingblock and interleaves the generated bits according to a range extensioncoding scheme to generate 24 bits to be included in an OFDM symbol. Inone such embodiment, the 24 bits correspond to 24 data tones generatedusing an FFT of size 32 at the IDFT processing unit 1818.

Similar to the block coder 1704 of FIG. 17A, the range extension codingscheme used by the block coder 1808 to generate the signal field of arange extension mode data unit, depending on an embodiment, is the sameas or different from the range extension coding scheme used by the blockcoder 1808 to generate the data portion of the range extension mode dataunit. In various embodiments, the block coder 1808 implements a “blocklevel” repetition scheme or a “bit level” repetition scheme as discussedabove in regard to the block coder 1704 of FIG. 17A. Similarly, inanother embodiment, the block coder 1808 generates m number of copies ofthe incoming bits and interleaves the resulting bit stream according toa suitable code, or otherwise encodes incoming bits or incoming blocksof bits using any suitable code, e.g., a Hamming block code with thecoding rate of a 1/2, 1/4, etc., or any other block code with the codingrate of 1/2, 1/4, etc. (e.g., (1,2) or (1, 4) block code, (12,24) blockcode or (6, 24) block code, a (13,26) block code, etc.). The effectivecoding rate for data units generated by the PHY processing unit 1800 isa product of the coding rate used by the FEC encoder 1806 and the numberof repetitions (or the coding rate) used by the block coder 1808,according to an embodiment.

In an embodiment, the block coder 1808 provides sufficient diversitygain such that no further interleaving of coded bits is needed, and theinterleaver 1810 is omitted. One advantage of omitting the interleaver1810 is that in this case OFDM symbols with 52 data tones can begenerated using 4× or a 6× repetition schemes even though in some suchsituations the number of data bits per symbol is not an integer. Forexample, in one such embodiment, the output of the FEC encoder 1806 ispartitioned into blocks of 13 bits and each block is repeated four times(or block encoded with a rate of 1/4) to generate 52 bits to be includedin an OFDM symbol. In this case, if the FEC encoder 1806 utilizes acoding rate of 1/2, the number of data bits per symbol is equal 6.5. Inan example embodiment utilizing 6× repetition, the FEC encoder 1806encodes information bits using a coding rate of 1/2 and the output ispartitioned into blocks of four bits. The block coder 1808 repeats eachfour bit block six times (or block encodes each block using a codingrate of 1/6) and adds four padding bits to generate 52 bits to beincluded in an OFDM symbol.

As in the example of the PHY processing unit 1700 of FIG. 17A discussedabove, if padding is used by the PHY processing unit 1800, the number ofdata bits per symbol (N_(DBPS)) used for padding bit computations is theactual number of non-redundant data bits in an OFDM symbol (e.g., 6bits, 12 bits, 13 bits as in the example above, or any other suitablenumber of bits). The number of coded bits per symbol (N_(CBPS)) used inpadding bit computations is equal to the number of bits actuallyincluded in an OFDM symbol (e.g., 24 bits, 48 bits, 52 bits, or anyother suitable number of bits included in an OFDM symbol).

Also as in the example of the PHY processing unit 1700 of FIG. 17, anumber of tail bits are typically inserted into each field of a dataunit for proper operation of the FEC encoder 1806, e.g., to ensure thatthe BCC encoder, after having encoded each field, is brought back tozero state. In one embodiment, for example, six tail bits are insertedat the end of the data portion before the data portion is provided tothe FEC encoder 1806 (i.e., after processing by the block coder 1704 isperformed). Similarly, in the case of a signal field, tail bits areinserted at the end of the signal field before the signal field isprovided to the FEC encoder 1806, according to an embodiment. In anexample embodiment in which the block coder 1808 utilizes a 4×repetition scheme (or another block code with the coding rate of 1/4),the FEC encoder 1806 utilizes the coding rate of 1/2, and the signalfield includes 24 information bits (including tail bits), the 24 signalfield bits are BCC encoded to generate 48 BCC encoded bits which arethen partitioned into four blocks of 12 bits each for further encodingby the block coder 1808. Accordingly, in this embodiment, the signalfield is transmitted over four OFDM symbols each of which includes 6information bits of the signal field.

Further, in some embodiments, the PHY processing unit 1800 generatesOFDM symbols with 52 data tones according to the MCSO specified in theIEEE 802.11n Standard or the IEEE 802.11ac Standard and the block coder1808 utilizes a 4× repetition scheme. In some such embodiments, extrapadding is used to ensure that the resulting encoded data stream to beincluded in an OFDM symbol includes 52 bits. In one such embodiment,padding bits are added to coded information the bits after the bits havebeen processed by the block coder 1808.

In the embodiment of FIG. 18A, the PHY processing unit 1800 alsoincludes a peak to average power ratio (PAPR) reduction unit 1809. In anembodiment, the PAPR reduction unit 1809 flips the bits in some or allrepeated blocks to reduce or eliminate the occurrence of the same bitsequences at different frequency locations in an OFDM symbol therebyreducing the peak to average power ratio of the output signal. Ingeneral, bit flipping involves changing the bit value of zero to the bitvalue of one and changing the bit vale of one to the bit value of zero.According to an embodiment, the PAPR reduction unit 1809 implements bitflipping using an XOR operation. For example, in an embodiment utilizing4× repetition of a block of coded bits, if a block of coded bits to beincluded in an OFDM symbols is denoted as C and if C′=C XOR 1 (i.e.,block C with bits flipped), then some possible bit sequences at theoutput of the PAPR reduction unit 1809, according to some embodiments,are [C C′ C′ C′], [C′ C′ C′ C], [C C′ C C′], [C C C C′], etc. Ingeneral, any combination of block with bits flipped and blocks with bitsnot flipped can be used. In some embodiments, the PAPR unit 1809 isomitted.

FIG. 18B is a block diagram of an example PHY processing unit 1850 forgenerating range extension mode data units, according to anotherembodiment. In some embodiments, the PHY processing unit 1850 generatessignal and/or data fields of range extension mode data units. Referringto FIG. 1, the AP 14 and the client station 25-1, in one embodiment,each include a PHY processing unit such as the PHY processing unit 1850.

The PHY processing unit 1850 is similar to the PHY processing unit 1800of FIG. 18, except that in the PHY processing unit 1850, the FEC encoder1806 is replaced by the LDPC encoder 1856. Accordingly, in thisembodiment, information bits are first encoded by the LDPC encoder 1856and the LDPC coded bits are then replicated or otherwise block encodedby the block coder 1808. In an embodiment, the LDPC encoder 1856utilizes a block code corresponding to a coding rate of 1/2, or a blockcode corresponding to another suitable coding rate. In the illustratedembodiment, the PHY processing unit 1850 omits the interleaver 1810because adjacent bits in an information stream are generally spread outby the LDPC code itself and, according to an embodiment, no furtherinterleaving is needed. Additionally, in an embodiment, furtherfrequency diversity is provided by the LDPC tone remapping unit 1860.According to an embodiment, the LDPC tone remapping unit 1860 reorderscoded information bits or blocks of coded information bits according toa tone remapping function. The tone remapping function is generallydefined such that consecutive coded information bits or blocks ofinformation bits are mapped onto nonconsecutive tones in the OFDM symbolto facilitate data recovery at the receiver in cases in whichconsecutive OFDM tones are adversely affected during transmission. Insome embodiments, the LDPC tone remapping unit 1860 is omitted.

FIG. 19A is a block diagram of an example PHY processing unit 1900 forgenerating range extension mode data units, according to anotherembodiment. In some embodiments, the PHY processing unit 1900 generatessignal and/or data fields of range extension mode data units. Referringto FIG. 1, the AP 14 and the client station 25-1, in one embodiment,each include a PHY processing unit such as the PHY processing unit 1900.

The PHY processing unit 1900 is similar to the PHY processing unit 1800of FIG. 18A except that in the PHY processing unit 1900 the block coder1916 is located after the constellation mapper 1914. Accordingly, inthis embodiment, BCC encoded information bits, after having beenprocessed by the interleaver 1910, are mapped to constellation symbolsand the constellation symbols are then replicated or otherwise blockencoded by the block coder 1916. According to an embodiment, processingby the FEC encoder 1906 is performed continuously over the entire fieldbeing generated (e.g., the entire data field, the entire signal field,etc.). In this embodiment, information bits corresponding to the fieldbeing generated are first encoded by the FEC encoder 1806 and the BCCcoded bits are then mapped to constellation symbols by the constellationmapper 1914. The constellation symbols are then partitioned into blocksof a specified size (e.g., 6 symbols, 12 symbols, 13 symbols, or anyother suitable number of symbols) and each block is then processed bythe block coder 1916. As an example, in an embodiment utilizing 2×repetition, the constellation mapper 1914 generates 24 constellationsymbols and the block coder 1916 generates two copies of the 24 symbolsto generate 48 symbols corresponding to 48 data tones of an OFDM symbol(e.g., as specified in the IEEE 802.11a Standard). As another example,in an embodiment utilizing 4× repetition, the constellation mapper 1914generates 12 constellation symbols and the block coder 1916 generatesfour copies of the 12 constellation symbols to generate 48 symbolscorresponding to 48 data tones of an OFDM symbol (e.g., as specified inthe IEEE 802.11a Standard). As yet another example, in an embodimentutilizing 2× repetition, the constellation mapper 1914 generates 26constellation symbols and the block coder 1916 repeats the 26 symbols(i.e., generates two copies of the 26 symbols) to generate 52 symbolscorresponding to 52 data tones of an OFDM symbol (e.g., as specified inthe IEEE 802.11n Standard or the IEEE 802.11ac Standard). In general, invarious embodiments and/or scenarios, the block coder 1916 generates anysuitable number of copies of blocks of incoming constellation symbolsand interleaves the generated symbols according to any suitable codingscheme. Similar to the block coder 1704 of FIG. 17A and the block coder1808 of FIG. 18A, the range extension coding scheme used by the blockcoder 1916 to generate a signal field (or signal fields) of a rangeextension mode data unit is, depending on the embodiment, the same as ordifferent from the range extension coding scheme used by the block coder1916 to generate the data portion of the range extension mode data unit.The effective coding rate for data units generated by the PHY processingunit 1900 is a product of the coding rate used by the FEC encoder 1906and the number of repetitions (or the coding rate) used by the blockcoder 1916, according to an embodiment.

According to an embodiment, because redundancy in this case isintroduced after the information bits have been mapped to constellationsymbols, each OFDM symbol generated by the PHY processing unit 1900includes less non-redundant data tones compared to OFDM data tonesincluded in a regular mode data units. Accordingly, the interleaver 1910is designed to operate on fewer tones per OFDM symbol compared to theinterleaver used in the regular mode (such as the interleaver 1610 ofFIG. 16), or the interleaver used in generating the corresponding shortrange data unit. For example, in an embodiment with 12 non-redundantdata tones per OFDM symbol, the interleaver 1910 is designed using thenumber of columns (N_(col)) of 6 and the number of rows (N_(row)) of2*the number of bits per subcarrier (N_(bpscs)). In another exampleembodiment with 12 non-redundant data tones per OFDM symbol, theinterleaver 1910 is designed using N_(col)of 4 and N_(row) of3*N_(bpscs). In other embodiments, other interleaver parametersdifferent from interleaver parameter used in the regular mode areutilized for the interleaver 1910. Alternatively, in an embodiment, theblock coder 1916 provides sufficient diversity gain such that no furtherinterleaving of coded bits is needed, and the interleaver 1910 isomitted. In this case, as in the example embodiment utilizing the PHYprocessing unit 1800 of FIG. 18A, OFDM symbols with 52 data tones can begenerated using 4× or a 6× repetition schemes even though in some suchsituations the number of data bits per symbol is not an integer.

As in the example embodiment of the PHY processing unit 1700 of FIG. 17Aor the PHY processing unit 1800 of FIG. 18A discussed above, if paddingis used by the PHY processing unit 1900, the number of data bits persymbol (N_(DBPS)) used for padding bit computations is the actual numberof non-redundant data bits in an OFDM symbol. (e.g., 6 bits, 12 bits, 13bits as in the example above, or any other suitable number of bits). Thenumber of coded bits per symbol (N_(CBPS)) used in padding bitcomputations is equal to the number of non-redundant bits included in anOFDM symbol which, in this case, corresponds to number of bits in theblock of constellation symbols processed by the block coder 1916 (e.g.,12 bits, 24 bits, 26 bits, etc.).

In some embodiments, the PHY processing unit 1900 generates OFDM symbolswith 52 data tones according to the MCSO specified in the IEEE 802.11nStandard or the IEEE 802.11ac Standard and the block coder 1916 utilizesa 4× repetition scheme. In some such embodiments, extra padding is usedto ensure that the resulting encoded data stream to be included in anOFDM symbol includes 52 bits. In one such embodiment, padding bits areadded to coded information the bits after the bits have been processedby the block coder 1808.

In the embodiment of FIG. 19, the PHY processing unit 1900 includes apeak to average power ratio (PAPR) reduction unit 1917. In anembodiment, the peak to average power ratio unit 1917 adds a phase shiftto some of the data tones modulated with repeated constellations. Forexample, in one embodiment the added phase shift is 180 degrees. The 180degree phase shift corresponds to a sign flip of the bits that modulatethe data tones for which phase shifts are implemented. In anotherembodiment, the PAPR reduction unit 1917 adds a phase shift that isdifferent than 180 degrees (e.g., a 90 degree phase shift or any othersuitable phase shift). As an example, in an embodiment utilizing 4×repetition, if a block of 12 constellation symbols to be included in anOFDM symbols is denoted as C and if simple block repetition isperformed, the resulting sequence is [C C C C]. In some embodiments, thePAPR reduction unit 1917 introduces a sign flip (i.e., −C) or a 90degree phase shift (i.e., j*C) for some of the repeated blocks. In somesuch embodiments, the resulting sequence is, for example, [C −C −C −C],[−C −C −C −C], [C −C C −C], [C C C −C], [C j*C, j*C, j*C], or any othercombination of C, −C, j*C, and −j*C. In general, any suitable phaseshift can be introduced in any repeated block in various embodimentsand/or scenarios. In some embodiments, the PAPR reduction unit 1809 isomitted.

In some embodiments, the PHY processing unit 1900 generates OFDM symbolswith 52 data tones according to the MCSO specified in the IEEE 802.11nStandard or the IEEE 802.11ac Standard and the block coding 1916utilizes a 4× repetition scheme. In some such embodiments, extra pilottones are inserted to ensure that the resulting number of data and pilottones in an OFDM symbol is equal to 56 as specified in the short rangecommunication protocol. As an example, in an embodiment, six informationbits are BCC encoded at the coding rate of 1/2 and the resulting 12 bitsare mapped to 12 constellation symbols (BPSK). The 12 constellationsymbols modulate 12 data tones which are then repeated four times thegenerated 48 data tones. Four pilot tones are added as specified in theIEEE 802.11n Standard and 4 extra pilot tones are added to generate 56data and pilot tones.

FIG. 19B is a block diagram of an example PHY processing unit 1950 forgenerating range extension mode data units, according to anotherembodiment. In some embodiments, the PHY processing unit 1950 generatessignal and/or data fields of range extension mode data units.

Referring to FIG. 1, the AP 14 and the client station 25-1, in oneembodiment, each include a PHY processing unit such as the PHYprocessing unit 1950.

The PHY processing unit 1950 is similar to the PHY processing unit 1900of FIG. 19, except that in the PHY processing unit 1950, the FEC encoder1906 is replaced by the LDPC encoder 1956. Accordingly, in thisembodiment, LDPC encoded information bits are mapped to constellationsymbols by the constellation mapper 1914 and the constellation symbolsare then replicated or otherwise block encoded by the block coder 1916.In an embodiment, the LDPC encoder 1956 utilizes a block codecorresponding to a coding rate of 1/2, or a block code corresponding toanother suitable coding rate. In the illustrated embodiment, the PHYprocessing unit 1950 omits the interleaver 1910 because adjacent bits inan information stream are generally spread out by the LDPC code itselfand, according to an embodiment, no further interleaving is needed.Additionally, in an embodiment, further frequency diversity is providedby the LDPC tone remapping unit 1960. According to an embodiment, theLDPC tone remapping unit 1960 reorders coded information bits or blocksof coded information bits according to a tone remapping function. Thetone remapping function is generally defined such that consecutive codedinformation bits or blocks of information bits are mapped ontononconsecutive tones in the OFDM symbol to facilitate data recovery atthe receiver in cases in which consecutive OFDM tones are adverselyaffected during transmission. In some embodiments, the LDPC toneremapping unit 1960 is omitted.

In the embodiments described above with regard to FIGS. 17-19, the rangeextension mode introduces redundancy by repeating bits and/orconstellation symbols in frequency domain. Alternatively, in someembodiments, the range extension coding scheme includes OFDM symbolrepetition of the signal and/or data fields of range extension mode dataunits that is performed in time domain. For example, FIG. 20A is adiagram showing a 2× repetition of each OFDM symbol of HT-SIG1 andHT-SIG2 fields in a preamble of a range extension mode data unit,according to an embodiment. Similarly, FIG. 20B is a diagram showing a2× repetition of each OFDM symbol of the L-SIG field in a preamble of arange extension mode data unit, according to an embodiment. FIG. 20C isa diagram showing a time domain repetition scheme for OFDM symbols inthe data portion of a control mode data unit, according to oneembodiment. FIG. 20D is a diagram showing a repetition scheme for OFDMsymbols in the data portion, according to another embodiment. As shown,in the embodiment of FIG. 20C OFDM symbol repetitions are outputcontinuously, while in the embodiment of FIG. 20D OFDM symbolrepetitions are interleaved. In general, OFDM symbol repetitions areinterleaved according to any suitable interleaving scheme, in variousembodiments and/or scenarios.

FIG. 21 is a flow diagram of an example method 2100 for generating adata unit, according to an embodiment. With reference to FIG. 1, themethod 2100 is implemented by the network interface 16, in anembodiment. For example, in one such embodiment, the PHY processing unit20 is configured to implement the method 2100. According to anotherembodiment, the MAC processing 18 is also configured to implement atleast a part of the method 2100. With continued reference to FIG. 1, inyet another embodiment, the method 2100 is implemented by the networkinterface 27 (e.g., the PHY processing unit 29 and/or the MAC processingunit 28). In other embodiments, the method 2100 is implemented by othersuitable network interfaces.

At block 2102, information bits to be included in the data unit areencoded according to a block code. In one embodiment, information bitsare encoded using a block level or a bit level repetition schemedescribed above with respect to the block coder 1704 of FIG. 17, forexample. At block 2104, the information bits are encoded using an FECencoder, such as the FEC encoder 1706 of FIG. 17A, or the LDPC encoder1756 of FIG. 17B, for example. At block 2106, information bits aremapped to constellation symbols. At block 2108, a plurality of OFDMsymbols is generated to include the constellation points. At block 2110,the data unit is generated to include the OFDM symbols.

In one embodiment, as illustrated in FIG. 21, information bits areencoded using a block encoder first (block 2102) and the block codedbits are then encoded using a FEC encoder (block 2104), such asdescribed above with respect to FIG. 17A, for example. In anotherembodiment, the order of blocks 2102 and 2104 is interchanged.Accordingly, in this embodiment, information bits are FEC encoded firstand the FEC encoded bits are encoded according to a block coding scheme,such as described above with respect to FIG. 18A, for example. In yetanother embodiment, block 2102 is positioned after block 2106. In thisembodiment, information bits are FEC encoded at block 2104, the FECencoded bits are mapped to constellation symbols at block 2106, and theconstellation symbols are then encoded according to a block coding orrepetition scheme, such as described above with respect to FIG. 19A, forexample, at block 2102.

In various embodiments, the range extension coding scheme uses a reducedsize fast Fourier transform (FFT) technique that outputs a reducednumber of constellation symbols which are repeated over an overallbandwidth to improve range and/or SNR performance. For example, in anembodiment, a constellation mapper maps a sequence of bits to aplurality of constellation symbols corresponding to 32 subcarriers(e.g., a 32-FFT mode) having 24 data tones. The 32 sub-carrierscorrespond to a 10 MHz sub-band of an overall 20 MHz bandwidth. In thisexample, the constellation symbols are repeated across the overallbandwidth of 20 MHz to provide redundancy of the constellation symbols.In various embodiments, the reduced size FFT technique is used incombination with the bit-wise and/or symbol replication techniquesdescribed above with regard to FIGS. 17-19.

In some embodiments where additional bandwidth is available, such as 40MHz, 80 MHz, 160 MHz, 320 MHz, 640 MHz, etc., the 32 subcarriers arerepeated across each 10 MHz sub-band of the overall bandwidth. Forexample, in another embodiment, a 32-FFT mode corresponds to a 5 MHzsub-band of an overall 20 MHz bandwidth. In this embodiment, theplurality of constellations are repeated 4x across the overall 20 MHzbandwidth (i.e., in each 5 MHz sub-band). Accordingly, a receivingdevice combines the multiple constellations to improve decodingreliability of the constellations. In some embodiments, the modulationof different 5 or 10 MHz sub-bands signals is rotated by differentangles. For example, in one embodiment, a first sub-band is rotated0-degrees, a second sub-band is rotated 90-degrees, a third sub-band isrotated 180-degrees, and a fourth sub-band is rotated 270-degrees. Inother embodiments, different suitable rotations are utilized. Thedifferent phases of the 20 MHz sub-band signals result in reduced peakto average power ratio (PAPR) of OFDM symbols in the data unit, in atleast some embodiments.

FIG. 22A is a diagram of a 20 MHz overall bandwidth having 2×repetitions of the range extension data unit having a 10 MHz sub-band,according to an embodiment. As shown in FIG. 22A, each sub-band of 10MHz is rotated by a rotation r1 and r2, respectively. FIG. 22B is adiagram of a 40 MHz overall bandwidth having 4× repetitions of the rangeextension data unit having the 10 MHz sub-band, according to anembodiment. As shown in FIG. 22B, each sub-band of 10 MHz is rotated bya rotation r1, r2, r3, and r4, respectively. FIG. 22C is a diagram of anexample tone plan 2230 for a 32-FFT mode that corresponds to a 10 MHzsub-band, according to an embodiment. The tone plan 2230 includes 32total tones, having 24 data tones, 2 pilot tones at indices +7 and −7, 1direct current tone, and 5 guard tones as shown in FIG. 22. Inembodiments where the reduced size FFT technique is used, thecorresponding tone plan is used for the HEW-LTF field, when present. Inother embodiments where the reduced size FFT technique is used but theHEW-LTF field is not present, the L-LTF field 704 is modified to includeadditional ±1 signs for pilot tones to the corresponding indices of themodified tone plan. For example, in an embodiment, tones −29, −27, +27,and +29 are added to the tone plan for the L-LTF field. In a furtherembodiment, ±1 signs are removed from the L-LTF tone plan in tones −2,−1, 1, and 2 in the 20 MHz bandwidth. Similar changes are applied foroverall bandwidths of 40 MHz, 80 MHz, 160 MHz, etc.

FIG. 23 is a diagram of an example data unit 2300 in which the rangeextension mode is used for a preamble 2301 of the data unit, accordingto an embodiment. In some embodiments, the preamble 2301 indicates boththe regular mode and the range extension mode. In such an embodiment,another method to differentiate the regular mode from the rangeextension mode is used, such as those described above with regard toFIGS. 9, 10, and 11.

The data unit 2301 is generally similar to and includes like-numberedelements with the data unit 1150 of FIG. 11B, except that the preamble2301 of the data unit 2300 is formatted differently from the preamble1151 of the data unit 1101. In an embodiment, the preamble 2301 isformatted such that a receiving device that operates according to theHEW communication protocol is able to determine that the preamble 2301is a range extension mode preamble rather than a regular mode preamble.In an embodiment, the preamble 2301 includes a modified long trainingfield M-LTF 2304 and a modified signal field M-SIG 2306 in place of theL-LTF 704 and the L-SIG 706, respectively, as compared to the data unit1151. In an embodiment, the preamble 2301 includes the L-STF 702, adouble guard interval followed by two repetitions of a modified longtraining sequence as the M-LTF 2304, a normal guard interval, and themodified signal field M-SIG. In some embodiments, the preamble 2301further includes one or more first HEW signal fields (HEW-SIGAs) 1152.In an embodiment, the preamble 2301 further includes one or moresecondary L-SIG(s) 1154 that follow the M-SIG field 2306. The secondaryL-SIG(s) 1154 are followed by a second L-LTF field (L-LTF2) 1156, insome embodiments. In other embodiments, the preamble 2301 omits theL-SIG(s) 1154 and/or the L-LTF2 1156. In some embodiments, the preamble2301 also includes an HEW-STF 1158, one or more HEW-LTF fields 1160, anda second HEW signal field (HEW-SIGB) 1162. In other embodiments, thepreamble 2301 omits the HEW-STF 1158, the HEW-LTF(s) 1160 and/or theHEW-SIGB 1162. In an embodiment, the data unit 2300 also includes a dataportion 716 (not shown in FIG. 23). In some embodiments, the HEW signalfields (HEW-SIGAs) 1152 are modulated using a same range extensioncoding scheme as the data field 716.

In various embodiments, the M-LTF 2304 corresponds to the L-LTF 704multiplied by a predetermined sequence (e.g., a polarization code). Forexample, using an index i, an i-th constellation symbol of the L-LTF 704is multiplied by an i-th value (e.g., ±1) of the predetermined sequenceto obtain the M-LTF 2304, as shown in Equation 1:M-LTF_(i) =C _(i) *L-LTF_(i)  (Equation 1)where C is the predetermined sequence. In some embodiments, the M-SIG2306 corresponds to the L-SIG 706 multiplied by the predeterminedsequence, as shown in Equation 2:M-SIG_(i) =C _(i) *L-SIG_(i)  (Equation 2)

In some embodiments, a length (i.e., a number of values) of thepredetermined sequence is equal to a sum of a number of data tones and anumber of pilot tones per 20 MHz band in the IEEE 802.11ac protocol, forexample 52 values (i.e., for 48 data tones and 4 pilot tones).

In an embodiment, the predetermined sequence and the modified longtraining sequence each have a length that is greater than or equal tothe sum of the number of data tones and the number of pilot tones. Asdescribed above with regard to the tone plan 2230 for a 32-FFT mode thatcorresponds to a 10 MHz sub-band, if the HEW-STF and/or HEW-LTF fieldsdo not exist in the range extension preamble, the receiver relies uponthe L-LTF field for demodulation of subsequent fields. In an embodiment,a tone plan miss-match between the 20 MHz L-LTF and the 10 MHz 32-FFTmode is corrected by inserting +1 or −1 signs in the L-LTF for themissing tones (e.g., tones −29, −27, +27, and +29 for a total of 58tones).

FIG. 24 is a block diagram of an example PHY processing unit 2400 forgenerating range extension mode data units, according to anotherembodiment. In some embodiments, the PHY processing unit 2400 generatessignal and/or training fields of range extension mode data units.Referring to FIG. 1, the AP 14 and the client station 25-1, in oneembodiment, each include a PHY processing unit such as the PHYprocessing unit 2400.

The PHY processing unit 2400 is similar to the PHY processing unit 1700of FIG. 17A, except that in the PHY processing unit 2400 a tonemultiplier 2404 is located after the constellation mapper 1614. In someembodiments, the tone multiplier 2404 generates i) modifiedconstellation symbols for the L-SIG field (i.e., M-SIG 2306) and ii) amodified long training sequence for the L-LTF field (i.e., M-LTF 2304)of a range extension mode data unit.

In some embodiments, the PHY processing unit 2400 is configured togenerate a first long training sequence for the range extension modepreamble at least by multiplying the predetermined sequence with asecond long training sequence of a second communication protocol. In anembodiment, for example, the tone multiplier 2404 multiplies thepredetermined sequence by the L-LTF 704 to obtain the M-LTF 2304. Thetone multiplier 2404 provides the M-LTF 2304 to the IDFT 1618 in placeof the L-LTF 704 during the range extension mode, in an embodiment.

In an embodiment, the tone multiplier 2404 receives constellationsymbols for data to be included in the L-SIG 706 from the constellationmapper 1614 and receives constellation symbols for pilot tones from apilot tone generator 2408. Accordingly, the M-SIG 2306 output from thetone multiplier 2404 includes modified constellation symbols for datatones and pilot tones to be converted into a time-domain signal by theIDFT 1618, in an embodiment.

In some embodiments, a receiver device decodes the M-SIG 2306, forexample, using channel estimates based on the M-LTF 2304. In thisexample, because both the L-LTF 704 and L-SIG 706 have been multipliedby the predetermined sequence, the legacy receiver device effectivelyremoves the multiplication as part of a channel estimation process orauto-correlation process. In an embodiment, a receiving devicedetermines whether a preamble corresponds to the range extension modepreamble 2400 or to the normal mode preamble 1101 by detecting whetherthe LTF field (e.g., either the M-LTF 2304 or the L-LTF 704) in thepreamble is generated with (e.g., multiplied by) the predeterminedsequence or without multiplying with the predetermined sequence based onauto-correlation of the L-LTF field with and without multiplication withthe predetermined sequence. In an embodiment, the receiving deviceperforms a first auto-correlation of the LTF with the L-LTF 704,performs a second auto-correlation of the LTF with the M-LTF 2304, andperforms a comparison of the auto-correlation results. Ifauto-correlation with the M-LTF 2304 produces a greater result comparedto the result of the auto-correlation with the L-LTF 704, then thereceiving device determines that the preamble corresponds to the rangeextension mode preamble 2300, in an embodiment. On the other hand, ifauto-correlation of the LTF with the L-LTF 704 produces a greater resultcompared to the result of auto-correlation with the M-LTF 2304, then thereceiving device determines that the preamble corresponds to the regularmode preamble 1101, in an embodiment. The receiver device performs theauto-correlation in the frequency domain, in some embodiments, accordingto Equation 3:max_(L)|Σ_(i)y_(i)L_(i)y_(i+1)*L_(i+1)|  (Equation 3)where y_(i) is a final received and averaged L-LTF sequence, L_(i) isthe transmitted L-LTF sequence belonging to IEEE 802.11a/n/ac or themodified long training sequence M-LTF. For example, L_(i) is eitherC_(i)* L-LTF_(i) for the range extension mode or L-LTF_(i) for theregular mode. In some scenarios, cross correlation of successive tonesgenerally removes channel effects and frequency domain match filteringfinds the most likely transmitted sequence. In some embodiments, thereceiver device uses channel estimation from the M-LTF to decodeadditional fields of the data unit (i.e., HEW-SIG and/or data fields).In some scenarios, the values of the predetermined sequencecorresponding to pilot tones are all one, allowing phase tracking on thepilot tones.

In some embodiments, OFDM modulation with reduced tone spacing is usedwith a same size FFT to reduce the data rate in the range extensionmode. For example, whereas the regular mode for a 20 MHz bandwidth OFDMdata unit uses a 64-point fast Fourier transform (FFT), resulting in 64OFDM tones, the range extension mode uses a reduced tone spacing by afactor of 2, resulting in 128 OFDM tones in the same bandwidth. In thiscase, tone spacing in the range extension mode OFDM symbols is reducedby a factor of two (1/2) compared to the regular mode OFDM symbols whileusing a same 64-point FFT, a 2× increased symbol duration, and 2×increased guard interval, where the symbols are then repeated in theremaining bandwidth. As another example, whereas the regular mode for a20 MHz bandwidth OFDM data unit uses a 64-point fast Fourier transform(FFT) resulting in 64 OFDM tones, the range extension mode uses a 1/4reduced tone spacing for a 20 MHz OFDM data unit resulting in 256 OFDMtones in the same bandwidth. In this case, tone spacing in the rangeextension mode OFDM symbols is reduced by a factor of four (1/4)compared to the regular mode OFDM symbols while using a 4× increasedsymbol duration and 4× increased guard interval. In such embodiments,long GI duration of, for example, 1.6 μs is used. However, the durationof the information portion of the range extension mode OFDM symbol isincreased (e.g., from 3.2 μs to 6.4 μs), and the percentage of the GIportion duration to the total OFDM symbols duration remains the same, inan embodiment. Thus, in this case, loss of efficiency due to a longer GIsymbol is avoided, in at least some embodiments. In various embodiments,the term “long guard interval” as used herein encompasses an increasedduration of a guard interval as well as a decreased OFDM tone spacingthat effectively increases duration of the guard interval. In otherembodiments, tone spacing is reduced, guard intervals are increased, andsymbol duration is increased according to factors of 6, 8, or othersuitable values. In some embodiments, variations in tone spacing, guardintervals, and symbol duration are used in combination with block codingor symbol repetition, as described above.

The total signal bandwidth of data units for the range extension mode insome embodiments is 20 MHz. For example, increased signal bandwidth isnot likely to further increase the range or improve SNR performance. Insome embodiments, the range extension mode is configured to use an FFTsize up to 512 points. In such an embodiment, if tone-spacing is reducedby a factor of 4 for the range extension mode, then a total bandwidthfor the 512 FFT is 40 MHz, thus the range extension mode uses up to 40MHz signal bandwidth.

In other embodiments, the range extension mode is configured for up tothe largest available signal bandwidth (e.g., 160 MHz). In variousembodiments, for example, a ½ tone spacing corresponds to a 64 FFT for a10 MHz band, a 128 FFT for a 20 MHz band, a 256 FFT for a 40 MHz band, a512 FFT for a 80 MHz band, and a 1024 FFT for a 160 MHz band. In someembodiments, the reduced tone spacing is used in combination with asmaller FFT size. In various embodiments, shorter guard intervals areused with reduced tone spacing, for example, a normal guard intervalhaving a duration equal to 25% of a duration of an OFDM symbol and ashort guard interval having a duration equal to 1/9^(th) of an OFDMsymbol.

In some embodiments, the range extension mode uses a smaller tonespacing (i.e., ½, ¼, etc.). In such an embodiment, the same FFT sizerepresents a smaller bandwidth, for example, 1/2 tone spacingcorresponds to a 64 FFT over a 10 MHz band. In an embodiment, the toneplan within a same FFT size is the same for both the range extensionmode and the regular mode, for example, a 64 FFT in the range extensionmode uses a same tone plan as in a 64 FFT for 20 MHz in IEEE 802.11ac.FIG. 25A is a diagram of an example 20 MHz total bandwidth having ½ tonespacing, according to an embodiment. In this case, the indices for theoriginal DC tones of a legacy tone plan for each 64 FFT are now in themiddle of the 10 MHz sub-band, instead of in the middle of the total 20MHz bandwidth, and the indices for the original guard tones areproximate to the true DC tone. In some embodiments where the band usedfor a range extension mode data unit is less than 20 MHz, a non-legacytone plan includes additional data or pilot tones at the indices for theoriginal DC tones, because the indices will not overlap with the “trueDC tone,” because the smallest signal bandwidth is 20 MHz for the rangeextension mode or regular mode. In some embodiments, the non-legacy toneplan includes additional data tones in place of guard tones at the edgesof the legacy tone plan to keep a same number of populated tones.

In other embodiments, when the tone spacing is reduced, the impact froma direct current offset and carrier frequency offset (CFO) becomeslarger as compared to the regular mode. FIG. 25B is a diagram of anexample 20 MHz total bandwidth having ½ tone spacing, according to anembodiment. In some embodiments, additional zero tones are definedproximate to the direct current tone of a band for a non-legacy toneplan of the range extension mode as compared to the legacy tone plan ofthe same FFT size in the regular mode. In various embodiments, theadditional zero tones are defined only beyond a predetermined FFT sizeand/or tone spacing, for example, when the FFT size is greater than orequal to 128 with tone spacing reduced by ½, or when the FFT size isgreater than or equal to 256 with tone spacing reduced by ¼. In someembodiments, an increased number of guard tones is used for a non-legacytone plan for the range extension mode, for example, to maintain a sameabsolute guard space (e.g., absolute frequency space) at a band edge ascompared to the legacy tone plan of the regular mode. In this case, atotal number of data tones and pilot tones in the non-legacy tone planis less than the legacy tone plan. In some examples, the same absoluteguard space facilitates filter designs. In some embodiments, forexample, where the total number of data tones for the non-legacy toneplan is different from a same FFT size of the regular mode, PHYparameters for the FEC interleaver and/or LDPC tone mapper are redefinedfor the number of data tones of the non-legacy tone plan.

FIG. 26A is a diagram of a non-legacy tone plan 2600 for the rangeextension mode having a size 64 FFT and ½ tone spacing, according to anembodiment. In the non-legacy tone plan 2600, additional guard tones areincluded (i.e., guard tones −28, −27, +27, +28) as compared to a legacytone plan for the regular mode. In some embodiments, the 64 FFTpopulates the DC tone with either a pilot tone or data tone. FIG. 26B isa diagram of a non-legacy tone plan 2601 for the range extension modehaving a size 128 FFT and ½ tone spacing, according to an embodiment. Inthe non-legacy tone plan 2601, additional guard tones (i.e., guard tones−58, −57, +57, +58) and additional DC tones (i.e., DC tones −2, −1, 0,1, 2) are included as compared to a legacy tone plan for the regularmode. FIG. 26C is a diagram illustrating a non-legacy tone plan 2602 forthe range extension mode having a size 256 FFT and ½ tone spacing,according to an embodiment. In the non-legacy tone plan 2602, additionalguard tones (i.e., guard tones −122, −121, +121, +122) and additional DCtones (i.e., DC tones −2, −1, 0, 1, 2) are included as compared to alegacy tone plan for the regular mode. In other embodiments, additionalguard tones and/or DC tones are added to the non-legacy tone plans forthe range extension mode as compared to the regular mode.

FIG. 27 is a flow diagram of an example method 2700 for generating adata unit, according to an embodiment. With reference to FIG. 1, themethod 2700 is implemented by the network interface 16, in anembodiment. For example, in one such embodiment, the PHY processing unit20 is configured to implement the method 2700. According to anotherembodiment, the MAC processing 18 is also configured to implement atleast a part of the method 2700. With continued reference to FIG. 1, inyet another embodiment, the method 2700 is implemented by the networkinterface 27 (e.g., the PHY processing unit 29 and/or the MAC processingunit 28). In other embodiments, the method 2700 is implemented by othersuitable network interfaces.

At block 2702, first OFDM symbols for a data field are generated. Invarious embodiments, generating the OFDM symbols at block 2702 includesgenerating OFDM symbols of the data portion according to one of therange extension coding scheme that corresponds to the range extensionmode or the regular coding scheme that corresponds to the regular mode.In an embodiment, the range extension coding scheme includes the rangeextension coding schemes described above with respect to FIG. 10 (e.g.,reduced tone spacing). In another embodiment, the range extension codingscheme includes the range extension coding schemes described above withrespect to FIGS. 17-20 (e.g., bit-wise repetition or symbol repetition).In yet another embodiment, the range extension coding scheme includesthe range extension coding schemes described above with respect to FIG.22 (e.g., data unit repetition). In yet another embodiment, the rangeextension coding scheme includes a suitable combination of the rangeextension coding schemes described above with respect to FIGS. 10, FIGS.17-20, and FIG. 22.

In an embodiment, generating the OFDM symbols for the data portion ofthe PHY data unit according to the range extension coding schemeincludes: encoding a plurality of information bits using a forward errorcorrection (FEC) encoder (e.g., the FEC encoder 1706, 1806, or 1906) toobtain a plurality of encoded bits; mapping the plurality of encodedbits to a plurality of constellation symbols, for example, using theconstellation mapper 1614 or 1914; generating the OFDM symbols toinclude the plurality of constellation symbols, for example, using theIDFT 1618 or 1818. In an embodiment, generating the OFDM symbols furtherincludes performing one of: i) encoding the plurality of informationbits according to a block coding scheme (e.g., using the block coder1704), ii) encoding the plurality of encoded bits according to the blockcoding scheme (e.g., using the block coder 1808), or iii) encoding theplurality of constellation symbols according to the block coding scheme(e.g., using the block coder 1916). In another embodiment, generatingthe OFDM symbols for the data field includes generating the OFDM symbolsfor the data field to include a plurality of constellation symbols in afirst bandwidth portion of a channel bandwidth and a copy of theplurality of constellation symbols in a second bandwidth portion of thechannel bandwidth, for example, as described above with respect to FIG.22. In a further embodiment, the copy of the plurality of constellationsymbols is generated to include a predetermined phase shift.

At block 2704, a preamble of the data unit is generated. The preamblegenerated at block 2704 is generated to indicate whether at least thedata portion of the data unit generated at block 2702 is generated usingthe range extension coding scheme or the regular coding scheme. Invarious embodiments and/or scenarios, one of the preambles 701 (FIGS.9A, 10A), 751 (Figs, 9B, 10B), 1101 (FIG. 11A), 1151 (FIG. 11B), or 1401(FIG. 14A) is generated at block 1604. In other embodiments, othersuitable preambles are generated at block 2704.

In an embodiment, the preamble is generated to have i) a first portionthat indicates a duration of the PHY data unit and ii) a second portionthat indicates whether at least some OFDM symbols of the data portionare generated according to the range extension coding scheme. In afurther embodiment, the first portion of the preamble is formatted suchthat the first portion of the preamble is decodable by a receiver devicethat conforms to a second communication protocol (e.g., a legacycommunication protocol), but does not conform to the first communicationprotocol (e.g., the HEW communication protocol), to determine theduration of the PHY data unit based on the first portion of thepreamble.

In an embodiment, the preamble generated at block 2704 includes a CIindication set to indicate whether at least the data portion isgenerated using the range extension coding scheme or the regular codingscheme. In an embodiment, the CI indication comprises one bit. In anembodiment, a portion of the preamble, in addition to the data portion,is generated using the coding scheme indicated by the CI indication. Inanother embodiment, the preamble generated at block 2704 is formattedsuch that a receiving device can automatically detect (e.g., withoutdecoding) whether the preamble corresponds to a regular mode preamble orto a range extension mode preamble. In an embodiment, detection of therange extension mode preamble signals to the receiving device that atleast the data portion is generated using the range extension codingscheme.

In an embodiment, generating the preamble includes generating a secondportion of the preamble including second OFDM symbols for i) a shorttraining field according to the first communication protocol and ii) atleast one copy of the short training field, and generating third OFDMsymbols for i) a long training field according to the firstcommunication protocol and ii) at least one copy of the long trainingfield. In a further embodiment, the OFDM symbols for the data portion,the second OFDM symbols, and the third OFDM symbols have a same toneplan that is distinct from a tone plan for the first portion of thepreamble.

In another embodiment, block 2704 includes generating a first signalfield for the PHY data unit according to the second communicationprotocol (e.g., the legacy communication protocol) and generating asecond signal field as a copy of the first signal field to indicate thatat least some OFDM symbols of the data field are generated according tothe range extension mode. In a further embodiment, the first signalfield and the second signal field indicate that the duration of the PHYdata unit is a predetermined duration and the second signal field isusable by a receiver device that conforms to the first communicationprotocol as a supplemental training field. In another embodiment, thefirst signal field and the second signal field are decodable incombination by a receiver device that conforms to the firstcommunication protocol to increase a decoding reliability of the firstsignal field and the second signal field.

In an embodiment, the first portion of the preamble includes i) a legacyshort training field that conforms to the second communication protocol,ii) a non-legacy long training field, and iii) a legacy signal fieldthat conforms to the second communication protocol, and the secondportion of the preamble does not include any training fields. In thisembodiment, a first plurality of constellation symbols are generated forthe legacy short training field using a legacy tone plan that conformsto the second communication protocol, a second plurality ofconstellation symbols are generated for the non-legacy long trainingfield using a non-legacy tone plan; and the OFDM symbols for the datafield include a third plurality of constellation symbols generated usingthe non-legacy tone plan.

In an embodiment, OFDM symbols are generated for the first portion ofthe preamble as a legacy preamble, using a normal guard interval, thatconforms to the second communication protocol, and OFDM symbols aregenerated for the second portion of the preamble using a long guardinterval. In a further embodiment, OFDM symbols for a non-legacy signalfield and a non-legacy short training field of the second portion of thepreamble are generated using the normal guard interval, and OFDM symbolsfor the second portion of the preamble are generated for a non-legacylong training field using the long guard interval. In anotherembodiment, OFDM symbols are generated for a legacy signal field of thefirst portion of the preamble using the normal guard interval, and OFDMsymbols are generated for a non-legacy signal field of the secondportion of the preamble using a long guard interval. In an embodiment,the second portion of the preamble is decodable by receiver devices thatconform to the first communication protocol and the long guard intervalof the second preamble signals to the receiver devices that conform tothe first communication protocol that the PHY data unit conforms to therange extension mode. In yet another embodiment, OFDM symbols aregenerated for the second portion of the preamble, using the long guardinterval, for i) a non-legacy signal field and ii) a copy of a firstOFDM symbol for the non-legacy signal field. In an embodiment, OFDMsymbols are generated for each field of a plurality of fields of thesecond portion of the preamble to include i) a double guard interval,ii) a first OFDM symbol for the field, and iii) a second OFDM symbol forthe field that is a copy of the first OFDM symbol.

At block 2706, the data unit is generated to include the preamblegenerated at block 2704 and the data portion generated at block 2702. Inan embodiment, the PHY data unit is generated to include a double guardinterval according to the second communication protocol followed by thefirst portion of the signal field and the second portion of the signalfield, without a guard interval between the first signal field and thesecond signal field.

In some embodiments, at least the first portion of the preamble istransmitted with a transmission power boost as compared to the datafield to increase a decoding range of the first portion of the preamble.

In another embodiment, OFDM symbols for the data field are generatedusing a first tone spacing and a long guard interval, and OFDM symbolsfor the first portion of the preamble are generated using i) a secondtone spacing that is different from the first tone spacing, and ii) aregular guard interval. In a further embodiment, the second tone spacingof the first portion of the preamble is i) a legacy tone spacing thatconforms to the second communication protocol, and ii) an integermultiple of the first tone spacing of the data field, and the regularguard interval is a legacy guard interval that conforms to the secondcommunication protocol. In another embodiment, OFDM symbols for thesecond portion of the preamble are generated including i) at least afirst OFDM symbol using the legacy tone spacing and the legacy guardinterval and ii) at least a second OFDM symbol using the first tonespacing and the long guard interval. In yet another embodiment, the OFDMsymbols for the data field are generated using the first tone spacing toinclude a plurality of constellation symbols in a first bandwidthportion of a channel bandwidth and a copy of the plurality ofconstellation symbols in a second bandwidth portion of the channelbandwidth, and the first bandwidth portion and the second bandwidthportion have a same bandwidth. In a further embodiment, generating theOFDM symbols for the data field includes generating the copy of theplurality of constellation symbols to include a predetermined phaseshift.

In an embodiment, generating the OFDM symbols for the data fieldincludes generating the OFDM symbols for the data field using the firsttone spacing, the long guard interval, and a long symbol duration. In afurther embodiment, generating the OFDM symbols for the first portion ofthe preamble comprises generating OFDM symbols for the first portion ofthe preamble using the second tone spacing, the regular guard interval,and a regular symbol duration. In a further embodiment, the second tonespacing of the first portion of the preamble is i) a legacy tone spacingand ii) an integer n multiple of the first tone spacing of the datafield, the regular guard interval is a legacy guard interval, and thelong symbol duration is an integer n multiple of the regular symbolduration.

In another embodiment, generating the OFDM symbols for the data field ofthe PHY data unit according to the range extension mode includes:generating the OFDM symbols for the data field using a non-legacy tonespacing and a non-legacy tone plan that do not conform to the secondcommunication protocol; and generating the preamble comprises generatingOFDM symbols for the first portion of the preamble using a second tonespacing that is different from the non-legacy tone spacing and a legacytone plan that is different from the non-legacy tone plan. In a furtherembodiment, the non-legacy tone plan includes at least one guard tone inplace of a corresponding data tone of the legacy tone plan proximate toa direct current tone. In an embodiment, the non-legacy tone planincludes at least one data tone in place of a corresponding guard toneof the legacy tone plan such that the non-legacy tone plan and thelegacy tone plan have a same number of data tones. In anotherembodiment, the non-legacy tone plan includes fewer data tones than thelegacy tone plan and generating the OFDM symbols for the data fieldusing the non-legacy tone spacing and the non-legacy tone plan includesencoding information bits for the OFDM symbols using an error correctingcode based on a number of data tones of the non-legacy tone plan. In anembodiment, the error correcting code is a binary convolutional code. Inanother embodiment, the error correcting code is a low density paritycheck code.

FIG. 28 is a flow diagram of an example method 2800 for generating adata unit, according to an embodiment. With reference to FIG. 1, themethod 2800 is implemented by the network interface 16, in anembodiment. For example, in one such embodiment, the PHY processing unit20 is configured to implement the method 2800. According to anotherembodiment, the MAC processing 18 is also configured to implement atleast a part of the method 2800. With continued reference to FIG. 1, inyet another embodiment, the method 2800 is implemented by the networkinterface 27 (e.g., the PHY processing unit 29 and/or the MAC processingunit 28). In other embodiments, the method 2800 is implemented by othersuitable network interfaces.

At block 2802, a first plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols is generated for a first field of a preambleto be included in the PHY data unit, in an embodiment. In someembodiments, each OFDM symbol of the first plurality of OFDM symbolscorresponds to a first long training sequence of the first communicationprotocol that is obtained at least by multiplying a predeterminedsequence with a second long training sequence of a second communicationprotocol. At block 2804, a first plurality of information bits for asecond field of the preamble are encoded to generate a first pluralityof encoded bits, in an embodiment.

At block 2806, the first plurality of encoded bits are mapped to a firstplurality of constellation symbols, in an embodiment. At block 2808, afirst plurality of modified constellation symbols are generated,including multiplying the first plurality of constellation symbols bythe predetermined sequence, in an embodiment. At block 2810, a secondplurality of orthogonal frequency division multiplexing (OFDM) symbolsare generated to include the first plurality of modified constellationsymbols, in an embodiment. At block 2812, the preamble is generated toinclude the first plurality of OFDM symbols for the first field and thesecond plurality of OFDM symbols for the second field, in an embodiment.At block 2814, the PHY data unit is generated to include at least thepreamble.

In some embodiments, the first plurality of information bits includes afirst set of one or more information bits that indicate a duration ofthe PHY data unit, the preamble being formatted such that the preambleis decodable by a receiver device that conforms to the secondcommunication protocol, but does not conform to the first communicationprotocol, to determine the duration of the PHY data unit based on thepreamble. In an embodiment, an i-th value of the first long trainingsequence corresponds to an i-th value of the predetermined sequencemultiplied with a corresponding i-th value of the second long trainingsequence where i is an index.

In an embodiment, a length of the first long training sequence isgreater than or equal to a sum of a number of data tones and a number ofpilot tones in an OFDM symbol specified by the second communicationprotocol. In some embodiments, generating the first plurality ofmodified constellation symbols includes multiplying the predeterminedsequence by a plurality of pilot tone constellation symbols for thesecond communication protocol. In some embodiments, values of thepredetermined sequence that correspond to the plurality of pilot toneconstellation symbols have a value of 1. In an embodiment, values of thepredetermined sequence have a value of +1 or −1.

In some embodiments, generating the first plurality of OFDM symbolsincludes generating the first plurality of OFDM symbols such that anauto-correlation output for the first field generated by a receiver thatconforms to the first communication protocol will signal i) a first modeof the first communication protocol or ii) a second mode of the firstcommunication protocol to enable automatic detection of the first modeor the second mode by the receiver device. In an embodiment, the firstfield includes the first long training sequence. In another embodiment,the first field includes the second long training sequence.

In an embodiment, the method 2800 further includes: encoding a secondplurality of information bits for a data field of the PHY data unit togenerate a second plurality of encoded bits; mapping the secondplurality of encoded bits to a second plurality of constellationsymbols; generating a second plurality of modified constellationsymbols, including multiplying the predetermined sequence by the secondplurality of constellation symbols; generating a third plurality oforthogonal frequency division multiplexing (OFDM) symbols to include thesecond plurality of modified constellation symbols; and generating thedata field to include the third plurality of OFDM symbols, wheregenerating the PHY data unit includes generating the PHY data unit toinclude at least the preamble and the data field.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for generating a physical layer (PHY)data unit for transmission via a communication channel, the PHY dataunit conforming to an extended range mode of a wireless communicationprotocol, the method comprising: encoding, at a communication device, aplurality of information bits to generate a plurality of encoded bits;mapping, at the communication device, the plurality of encoded bits to aplurality of constellation symbols, including mapping each bit tomultiple constellation symbols; generating, at the communication device,a plurality of orthogonal frequency division multiplexing (OFDM) symbolscorresponding to the PHY data unit using the plurality of constellationsymbols, wherein the OFDM symbols are generated such that: the OFDMsymbols have a tone spacing that is ¼ of a tone spacing of a legacywireless communication protocol, and the OFDM symbols span only asubband of a 20 MHz communication channel; and generating, at thecommunication device, a transmission signal using the plurality of OFDMsymbols, the transmission signal spanning only the subband of the 20 MHzcommunication channel.
 2. The method of claim 1, wherein the wirelesscommunication protocol defines a normal mode that utilizes bandwidthsthat span at least the 20 MHz communication channel.
 3. The method ofclaim 1, wherein mapping the plurality of encoded bits to the pluralityof constellation symbols includes: mapping each bit to a respectivefirst constellation symbol; and mapping each bit to a respective secondconstellation symbol that is phase shifted with respect to therespective first constellation symbol.
 4. The method of claim 1, whereinmapping the plurality of encoded bits to the plurality of constellationsymbols includes: mapping each bit to a respective first constellationsymbol; and copying each first constellation symbol to a respectivesecond constellation symbol.
 5. The method of claim 4, wherein mappingthe plurality of encoded bits to the plurality of constellation symbolsfurther includes: applying a phase shift to each second constellationsymbol.
 6. The method of claim 1, wherein mapping the plurality ofencoded bits to the plurality of constellation symbols includes: mappingeach bit to two constellation symbols.
 7. An apparatus, comprising: anetwork interface device implemented using one or more integratedcircuit (IC) devices, including: a media access control (MAC) processingunit configured to operate according to a communication protocol thatdefines an extended range mode, the MAC processing unit implementedusing the one or more IC devices, and a physical layer (PHY) processingunit coupled configured to operate according to the communicationprotocol, the PHY processing unit coupled to the MAC processing unit andimplemented using the one or more IC devices; wherein the PHY processingunit is configured to: encode a plurality of information bits togenerate a plurality of encoded bits; map the plurality of encoded bitsto a plurality of constellation symbols, including mapping each bit tomultiple constellation symbols; generate a plurality of orthogonalfrequency division multiplexing (OFDM) symbols corresponding to a PHYdata unit using the plurality of constellation symbols, wherein the PHYdata unit conforms to the extended range mode, and wherein the OFDMsymbols are generated such that: the OFDM symbols have a tone spacingthat is ¼ of a tone spacing of a legacy wireless communication protocol,and the OFDM symbols span only a subband of a 20 MHz communicationchannel; and generate a transmission signal using the plurality of OFDMsymbols, the transmission signal spanning only the subband of the 20 MHzcommunication channel, wherein the transmission signal corresponds tothe PHY data unit.
 8. The apparatus of claim 7, wherein the wirelesscommunication protocol defines a normal mode that utilizes bandwidthsthat span at least the 20 MHz communication channel.
 9. The apparatus ofclaim 7, wherein mapping the plurality of encoded bits to the pluralityof constellation symbols includes: mapping each bit to a respectivefirst constellation symbol; and mapping each bit to a respective secondconstellation symbol that is phase shifted with respect to therespective first constellation symbol.
 10. The apparatus of claim 7,wherein mapping the plurality of encoded bits to the plurality ofconstellation symbols includes: mapping each bit to a respective firstconstellation symbol; and copying each first constellation symbol to arespective second constellation symbol.
 11. The apparatus of claim 10,wherein mapping the plurality of encoded bits to the plurality ofconstellation symbols further includes: applying a phase shift to eachsecond constellation symbol.
 12. The apparatus of claim 7, whereinmapping the plurality of encoded bits to the plurality of constellationsymbols includes: mapping each bit to two constellation symbols.
 13. Theapparatus of claim 7, wherein the PHY processing unit includes: one ormore transceivers.
 14. The apparatus of claim 13, further comprising:one or more antennas coupled to the one or more transceivers.
 15. Atangible, non-transitory computer readable medium, or media, storingmachine readable instructions that, when executed by one or moreprocessors, cause the one or more processors to: encode a plurality ofinformation bits to generate a plurality of encoded bits; map theplurality of encoded bits to a plurality of constellation symbols,including mapping each bit to multiple constellation symbols; generate aplurality of orthogonal frequency division multiplexing (OFDM) symbolscorresponding to physical layer (PHY) data unit using the plurality ofconstellation symbols, wherein the PHY data unit conforms to an extendedrange mode of a wireless communication protocol, and wherein the OFDMsymbols are generated such that: the OFDM symbols have a tone spacingthat is ¼ of a tone spacing of a legacy wireless communication protocol,and the OFDM symbols span only a subband of a 20 MHz communicationchannel; and generate a transmission signal using the plurality of OFDMsymbols, the transmission signal spanning only the subband of the 20 MHzcommunication channel, wherein the transmission signal corresponds tothe PHY data unit.
 16. The computer readable medium, or media, of claim15, wherein the wireless communication protocol defines a normal modethat utilizes bandwidths that span at least the 20 MHz communicationchannel.
 17. The computer readable medium, or media, of claim 15,further storing machine readable instructions that, when executed by oneor more processors, cause the one or more processors to: map each bit toa respective first constellation symbol; and map each bit to arespective second constellation symbol that is phase shifted withrespect to the respective first constellation symbol.
 18. The computerreadable medium, or media, of claim 15, further storing machine readableinstructions that, when executed by one or more processors, cause theone or more processors to: map each bit to a respective firstconstellation symbol; and copy each first constellation symbol togenerate a respective second constellation symbol.
 19. The computerreadable medium, or media, of claim 18, further storing machine readableinstructions that, when executed by one or more processors, cause theone or more processors to: apply a phase shift to each secondconstellation symbol.
 20. The computer readable medium, or media, ofclaim 15, further storing machine readable instructions that, whenexecuted by one or more processors, cause the one or more processors to:map each bit to two constellation symbols.